For the test it can be downloaded from Microsoft. I choose ver. 2016:
https://www.microsoft.com/en-us/evalcenter/download-windows-server-2016
Here I will not explain in detail the steps when creating a new virtual machine in VirtualBox, but it is important to enter the minimum requirements (parameters) for the relevant operating system.
I set:
- Disk space - 80 GB
- Base memory - 4 GB (4096 MB)
After creating the virtual machine in Settings -> Storage -> Optical drive load your Windows Server .ISO file
Then start the machine and install the server.
Look here:
https://www.microsoft.com/en-us/software-download/windows10
https://www.microsoft.com/en-us/software-download/windows11
The virtual machine is created in the same way. Then the .ISO file is added and the installation of the corresponding operating system is started.
If you want Windows 11 to have Internet during the installation,
you need first to set up DHCP and set up the Internet via NAT on the server.