Do you know about dosdude's Catalina patcher? And for previous versions? It's unofficial, so it might not suit you at all. It allows older hardware to run (with some caveats) newer macOS versions.
Re:The Mac “Pro”
by enev on Thursday December 12, 2019 @08:40AM
(#21771709)
Just an FYI, at least on previous patchers it turns off SIP. I’ve turned it back on and haven’t had an issue, but it does display a warning on boot that things may not work.
http://dosdude1.com/catalina/
Currently I have a 2009 MacBook Pro 5.1 running High Sierra.