my computer is not compatible with OS Catalina, i have a Mac Pro early 2008 model... What can I do in order to upgrade OS

Yes officially, El Capitan, but nudge, nudge, wink, wink look elsewhere

on the internet.

I've looked all over for the Report this Post button but can't find it! 😊

The early 2008 Mac Pro can be upgraded to OS X 10.11.6 but not to versions later than that.