Per core licensing is based on the number of logical processors a server has. A logical processor is either a physical core or a virtual core created by hyperthreading. Per core licensing requires purchasing a license for each logical processor on the server. Verified References: [Per core licensing], [Logical processor]

The server is not joined to the domain is causing the issue. A domain is a logical grouping of computers that share a common directory database and security policy on a network. Active Directory is a Microsoft technology that provides domain services for Windows-based computers. To use Active Directory credentials to log on to a server, the server must be joined to the domain that hosts Active Directory. If the server is not joined to the domain, it will not be able to authenticate with Active Directory and will only accept local accounts for logon. To join a server to a domain, the administrator must have a valid domain account with sufficient privileges and must know the name of the domain controller that hosts Active Directory.

* HTTPS (Secure Web Traffic): Port 443 is the standard port for HTTPS, which is essential for encrypting communication between web browsers and a secure website. (CompTIA Server+ Objectives SK0-004: 4.1)
* Why other options are not essential:
* 25 (SMTP): Used for email transmission
* 53 (DNS): Used for domain name resolution
* **3389 (RDP): ** Used for remote desktop connections
* **8080 (Alternate HTTP): ** Sometimes used for web servers, but not the standard secure port

A checksum is a value that is calculated from a data set to verify its integrity and authenticity. A checksum can be used to compare a downloaded installation package with the original source to ensure that the package has not been corrupted or tampered with during the download or transmission process. If the checksums match, then the package is safe to install. If the checksums do not match, then the package may be infected with malware or contain errors that could cause installation problems. Therefore, validating the checksum for the downloaded installation package is a necessary step before launching the installation again12
1: CompTIA Server+ Certification Exam Objectives 2: How to Verify File Integrity Using Checksums on Linux

An IDRAC (Integrated Dell Remote Access Controller) is a tool that can be used to command a remote shutdown of a physical Linux server. An IDRAC is a hardware device that provides out-of-band management for Dell servers. It allows the technician to access the server's console, power cycle, reboot, or shut down the server remotely using a web interface or a command-line interface. An IDRAC does not depend on the operating system or network connectivity of the server. A virtual serial console is a tool that can be used to access a remote virtual machine's console using a serial port connection. A KVM (Keyboard, Video, Mouse) switch is a device that allows the technician to switch between different computer sources using the same keyboard, monitor, and mouse. A crash cart is a mobile unit that contains a keyboard, monitor, mouse, and other tools that can be connected to a physical server for troubleshooting purposes. References:
https://www.dell.com/support/kbdoc/en-us/000131486/understanding-the-idrac
https://www.howtogeek.com/799968/what-is-a-kvm-switch/
https://www.techopedia.com/definition/1032/business-impact-analysis-bia