I can't download Xcode because my Mac mini is not up to date. However, there are no updates for my Mac mini. Is there anything to do? My Mac mini is currently is version 10.12.6. Xcode requires "version 10.14.4 or laterV. However, when I check for available updates for my OS, there are none
You can get earlier versions of Xcode from here:

https://developer.apple.com/download/more/?=xcode

This may be an option if you can't upgrade the OS.