Explanation
The two options that are available for the administrator to make the shortcut available to all desktop pool users, while minimizing ongoing administrative effort, before updating the desktop pool golden image are:
Copy the shortcut to c:\users\Public\Desktop. This option will place the shortcut in the public desktop folder, which is shared by all users who log on to the same computer. The public desktop folder is normally a hidden folder, so the administrator needs to enable the option to show hidden files and folders in File Explorer1. This option does not require any additional software or configuration, but it will only work for the existing desktops in the pool. If new desktops are added or refreshed, the shortcut will not be copied automatically.
Configure a Shortcut with DEM (Dynamic Environment Manager). This option will use the DEM console to create a shortcut configuration that will apply the shortcut to the user's desktop during logon2. The administrator needs to install and configure DEM on the Horizon environment, and create a configuration share and a profile archive share for storing the DEM settings3. This option requires more initial setup, but it will work for any desktop in the pool, regardless of whether it is new or refreshed. It also allows more flexibility and control over the shortcut properties and conditions.
The other options are not valid or feasible because:
Copying the shortcut during user provisioning to a non-writeable App Volume will not work because App Volumes are used to deliver applications, not shortcuts. App Volumes are virtual disks that are attached to the virtual machines at runtime, and they contain application files, registry entries, and settings4. Copying a shortcut to an App Volume will not make it appear on the user's desktop.
Copying the shortcut to the Windows Default Domain Controller Policy will not work because this policy is used to configure settings for domain controllers, not desktops. The Default Domain Controller Policy is a Group Policy Object (GPO) that is linked to the Domain Controllers organizational unit (OU) in Active Directory, and it contains security settings that are applied to all domain controllers in the domain5. Copying a shortcut to this policy will not affect any desktops in the Horizon environment.
Configuring a Shortcut with Horizon View Client will not work because Horizon View Client is used to connect to remote desktops and applications, not to create shortcuts. Horizon View Client is a software application that runs on various devices and platforms, and it allows users to access their virtual desktops and applications through a secure connection6. Configuring a shortcut with Horizon View Client will not make it appear on the user's desktop.
References:
How to make a desktop shortcut available for all users in Windows 101
VMware Dynamic Environment Manager (DEM) 2306 - Carl Stalhood2
VMware Tech Zone Antivirus Considerations in a VMware Horizon Environment: exclusions for Horizon View, App Volumes, User Environment Manager, ThinApp3 App Volumes Overview Default Domain Controller Policy5 VMware Horizon Clients Documentation6

In a load balanced Horizon POD with three Connection Servers, there are 450 active Blast sessions connected.
If one of these Connection Servers runs into an unplanned outage, only the active sessions from the failed Connection Server are disconnected, because HTTPS Secure Tunnel is disabled. This means that the other two Connection Servers can still handle the remaining sessions without interruption.
The HTTPS Secure Tunnel is a feature that allows Horizon Client devices to establish secure connections to virtual desktops and applications through the Connection Server. When this feature is enabled, all the display protocol traffic is tunneled through the Connection Server, which acts as a proxy between the client and the desktop. This increases the security and simplifies the network configuration, but also adds some overhead and dependency on the Connection Server availability1.
When this feature is disabled, the Horizon Client devices connect directly to the desktops using their IP addresses or hostnames, bypassing the Connection Server. This reduces the load and dependency on the Connection Server, but also requires more network configuration and firewall rules to allow direct access to the desktops2.
The Blast Secure Gateway is a similar feature that allows Horizon Client devices to establish secure connections to virtual desktops and applications using the Blast Extreme protocol through the Connection Server. When this feature is enabled, the Blast Extreme traffic is tunneled through the Connection Server, which acts as a gateway between the client and the desktop. When this feature is disabled, the Horizon Client devices connect directly to the desktops using Blast Extreme3.
In this scenario, both HTTPS Secure Tunnel and Blast Secure Gateway are disabled, which means that the Horizon Client devices connect directly to the desktops using Blast Extreme. Therefore, if one of the Connection Servers fails, only the sessions that were authenticated by that Connection Server are affected. The other sessions can continue without interruption, as long as they can reach their desktops directly4.
The other options are not correct for this scenario:
All 450 active sessions are disconnected, and have to re-connect again by the end-user. This would be true if HTTPS Secure Tunnel or Blast Secure Gateway were enabled, and all the display protocol traffic was tunneled through the Connection Server. In that case, any failure of a Connection Server would disconnect all the sessions that were using it as a proxy5.
All active sessions will stay connected, because HTTPS Secure Tunnel and Blast Secure Gateway are disabled. This would be true if there was no dependency on the Connection Server after authentication.
However, even with HTTPS Secure Tunnel and Blast Secure Gateway disabled, there is still some communication between the Horizon Client and the Connection Server for session management and heartbeat monitoring. If a Connection Server fails, these communications are lost and the sessions are terminated.
All 450 active session are logged off immediately. This would be true if there was a global setting in Horizon Console to log off users when a Connection Server fails. However, there is no such setting in Horizon Console. The default behavior is to disconnect users when a Connection Server fails, not log them off.
References:
Configuring HTTPS Secure Tunnel
Configuring Network Ports for Direct Connections
Configuring Blast Secure Gateway
Load Balancing Across Multiple Pods
Horizon 7: Monitoring health of Horizon Connection Server using Load Balancer
[Horizon 7 Pods]
[Global Settings for Client Sessions in Horizon Console]
[VMware Horizon Architecture Planning]

The user's problem is that their settings for the e-mail client are not being saved across sessions. This means that their user profile, which contains their personal data, settings, and preferences, is not being preserved or synchronized properly. To solve this problem, the administrator can deploy one or more of the following options to manage user profiles in Horizon:
VMware App Volumes Writable Volumes: This option allows users to store user-installed applications, data, and settings on a disk independent of the VM. Writable volumes can be attached to desktops along with application packages, and they can isolate the user-installed applications from the system-installed applications. Writable volumes can also be configured to capture specific files and registry keys by using the snapvol.cfg policy file. This option can help users retain their e-mail client settings on a writable volume that is attached to their desktop at each login.
Persona Management: This option allows administrators to manage user profiles by using a remote repository that stores user profiles. Persona Management synchronizes the user profile between the remote repository and the local desktop at login, logout, and at regular intervals during the session.
Persona Management also supports profile redirection, which allows administrators to redirect certain folders in the user profile to a network share or a writable volume. This option can help users access their e-mail client settings from the remote repository or the redirected folder at each login.
VMware Dynamic Environment Manager: This option allows administrators to manage user profiles and policies by using a central share that stores user configuration files. Dynamic Environment Manager captures and applies user settings and preferences based on conditions and triggers, such as location, device, or application launch. Dynamic Environment Manager also supports profile archives, which allow administrators to back up and restore user profiles on demand or on schedule. This option can help users apply their e-mail client settings from the central share or the profile archive at each login.
The other options are not valid options for managing user profiles in Horizon:
Roaming Profiles: This option is a native Windows feature that allows users to access their user profile from any computer in a domain by storing it on a network share. However, this option is not recommended for Horizon because it can cause long login times, profile corruption, and data loss due to its synchronous and overwrite behavior. Roaming profiles are also incompatible with instant clones and linked clones.
Flexible profiles: This option does not exist in Horizon or Windows. It might be confused with Flex Profiles, which is a third-party product from Liquidware that provides profile management solutions similar to Dynamic Environment Manager.
References: Writable Volumes Overview, Configuring User Profiles with Horizon Persona Management, VMware Dynamic Environment Manager Overview, and [VMware Horizon 8.x Professional Course]

Explanation

To deploy a RDS desktop pool with the new standard of Windows Server 2019, the steps should be ordered as follows:
Prepare the Windows Server 2019 golden image.This is the first step because you'll need a prepared OS image to base your RDS desktop pool on.
Add an Automated Farm.Once your golden image is ready, you can set up an automated farm for the RDS desktop pool.
Add a RDS desktop pool.Using the automated farm and the prepared golden image, you can now add the RDS desktop pool.
Entitle AD users and/or groups.With the RDS desktop pool in place, the next step is to give Active Directory (AD) users and groups the necessary entitlements to access the desktops.
Launch Horizon Client and verify access to RDS desktop.As the final verification step, launch the Horizon Client to ensure that you can access the newly created RDS desktop pool and that everything is functioning as expected.
So, the sequential order is: Prepare the Windows Server 2019 golden image -> Add an Automated Farm -> Add a RDS desktop pool -> Entitle AD users and/or groups -> Launch Horizon Client and verify access to RDS desktop.

To increase the capacity and resiliency of VMware Horizon desktop pools, deploying Horizon on VMware Cloud on AWS or in a remote data center are viable options. VMware Cloud on AWS provides a scalable and secure cloud platform, allowing for quick expansion and disaster recovery capabilities. Similarly, deploying Horizon in a remote data center can provide geographical diversity, reducing the impact of localized disasters and improving overall resilience.