To resolve the certificate mismatch error, you should reissue the client certificate with client authentication enabled. According to 2, when you use Azure certificate for authentication type on point-to-site VPN connections, you need to ensure that your client certificates have client authentication as one of their enhanced key usage attributes. Otherwise, you will receive a certificate mismatch error when connecting by using a VPN client.

The error message "Error getting auth token" occurs when you specify an incorrect password for the global administrator account provided at the beginning of the Azure AD Connect installation process To resolve this issue, you should check that you have specified the correct password for your global administrator account. If you have specified an incorrect password, update it and then restart the Azure AD Connect service

The proposed solution, which is to configure subnet delegation, does not meet the goal of making the new subnet unreachable from the on-premises network. Subnet delegation is a mechanism to delegate management of a subnet to another resource such as a Network Virtual Appliance or a Service Endpoint. It does not provide any means to restrict or isolate a subnet from the rest of the network.
To meet the goal, you can use Network Security Groups (NSGs) to restrict traffic to and from the new subnet. NSGs allow you to define inbound and outbound security rules that specify the type of traffic that is allowed or denied based on different criteria such as source or destination IP address, protocol, port number, etc. By creating a custom NSG and defining rules that deny traffic to and from the new subnet, you can effectively make that subnet unreachable from the on-premises network.
Therefore, the correct answer is option B, "No".
Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/security-overview
https://docs.microsoft.com/en-us/azure/virtual-network/network-security-groups-overview

According to Microsoft Azure's troubleshooting documentation, one of the steps to troubleshoot backup failures on Azure virtual machines is to check the Azure VM Guest Agent service health. You should ensure that the Azure VM Guest Agent service is started and up-to-date 1. On a Windows VM, you can navigate to services.msc and ensure that the Windows Azure VM Guest Agent service is up and running. Also, ensure that the latest version is installed 2