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).
I think this VM is still on Sonoma, actually. I still need to upgrade.
I can't remember exactly what I did to get an installer image, but there's a million shell scripts online for downloading macOS installer images. For booting it, I use this premade OpenCore for KVM/Proxmox. I have to check if I made other modifications (I run on an AMD CPU), but I think I mainly just had to set the serial and model - I personally used a 2019 Mac Pro.
Yes, I downloaded it, but just couldn't figure out how to turn it into a bootable installer ISO without an already working macos instance
I could be totally delusional, but I think it's just something like
dd if=whatchamacallit.dmg of=whatchamacallit.img. I think you can get a net install image through macrecovery, which is a utility included with OpenCore packages.