My little "spare" computer is a 2013 Sony Vaio that is WiFi only, one of the USB ports doesn't work and I haven't found a battery to replace the one it came with (so it has to stay plugged in all of the time). It arrived with Win 8, was updated to Win 10, and I don't know that I want to bother with Win 11 on it.

The Dell XPX I'm using now was purchased a couple of years ago and came with Win 10. The old HP Pavilion Elite HPE is a quad core I bought with Win 7 for all of the heavy duty Adobe software I use and it still has my most recent releases (from work, not purchased by me). It has Win 10 on it now. The only way to upgrade it is to format the whole things and get it back to talking to the network, but I'd lose all of the installed software. I have a full backup, but I don't think it would put the software back without insurmountable complications. I move data into and out using a transfer cable that acts like another drive on both computers and has a built in software called EasySuite.exe.

I got the cable on sale from the online folks at Radio Shack: it's still around, and still selling useful stuff - though as Joe points out, my other and more reliable place was Fry's Electronics and it has completely vanished. They didn't even do "Going Out Of Business" sales, they just turned off the website and padlocked the doors one day.