Half of these exist because I was bored once.
The Windows 10 and MacOS ones are GPU passthrough enabled and what I occasionally use if I have to use a Windows or Mac application. Windows 7 is also GPU enabled, but is more a nostalgia thing than anything.
I think my PopOS VM was originally installed for fun, but I used it along with my Arch Linux, Debian 12 and Testing (I run Testing on host, but I wanted a fresh environment and was too lazy to spin up a Docker or chroot), Ubuntu 23.10 and Fedora to test various software builds and bugs, as I don't like touching normal Ubuntu unless I must.
The Windows Server 2022 one is one I recently spun up to mess with Windows Docker Containers (I have to port an app to Windows, and was looking at that for CI). That all become moot when I found out Github's CI doesn't support Windows Docker containers despite supporting Windows runners (The organization I'm doing it for uses Github, so I have to use it).
10, plain 11, 7, and funny enough, Server 2022 are all legit licenses (I can get a key for server through my university). Actually, I'm pretty sure the 11 one, I upgraded a Windows 7 VM to 10, then to 11.
Every other Windows version that needs it (11 LTSC, 8.1, and Vista), I just temporarily host a phony KMS server whenever it needs to be reactivated.
I apologize for talking so much about Windows on a Linux sub. May Stallman break into my house and give me 10 lashes as I slumber.
The Windows XP and Windows 7 I have are also from my university, from a long long time ago.😃