Catalina or Mojave on Mac Pro mid 2012

https://www.apple.com/macos/catalina/

macOS Catalina - Technical Specifications - Apple Support

https://support.apple.com/kb/SP803?locale=en_US

System requirements macOS 10.15 Catalina

macOS Catalina will run on all Macintosh computers that supported Mojave:[1]

MacBook: Early 2015 or newer

MacBook Air: Mid 2012 or newer

MacBook Pro: Mid 2012 or newer

Mac Mini: Late 2012 or newer

iMac: Late 2012 or newer

iMac Pro

Mac Pro: Late 2013 or newer;

Mid 2010 or Mid 2012 if upgraded with a recommended Metal-capable GPU

You can ref: this thread for metal capable options: https://discussions.apple.com/thread/8418863?answerId=33491799022#33491799022

Here are the specs for all 5,1 Mac Pros:

https://everymac.com/ultimate-mac-lookup/?search_keywords=MacPro5,1

I looked at several and they seem to stop at 10.14 (Mojave). So, best you check your exact model.