I've installed Linux Mint on quite a few older Dell Optiplex computers and it works really well. Very fast, and much easier to manage than windows. So far, I've tried Optiplex, 745, 780, 7010 and 7040 machines, I'm using the latter one for daily use. Linux seems to be far more stable than Windows, you don't need a anti-virus software and it doesn't spy on your activity. Linux is FREE and easy to install, it's certainly worth looking at, especially as Microsoft will soon be forcing users to migrate onto windows 11.