Why is it so cheap?  Because it is the only Mac Mini that the RAM is soldered in and can not be upgraded.  I have tried OS X and OS 12 and it is painfully slow, unusably slow.  It came with OS X which was slow.  I bought it to learn iOS and macOS Xcode/Swift but you need at least OS 11 to download Xcode.  The simplest of operations such as opening system preferences or closing an app can take 10 - 30 seconds.Run away, little bird...Run far, far away!