Downgrading from Catalina to an earlier OS (...but not the pre upgrade OS)

I won't bore everyone with the backstory but having upgraded from Sierra to Catalina, I've discovered that my 32 bit Office 2011 package is no longer operable. Can I downgrade to High Sierra or Mojave? I don't want to go all the way back to Sierra because another application I run needs an OS later than 10.12... which is where this all began.

I have a Time Machine (Sierra) backup from immediately before I upgraded to Catalina and will make a new Time Machine (Catalina) backup on a different external drive before I do anything further.  Assuming I can reinstall to the last Sierra backup (plenty of online advice on that, including support.apple.com) can I then upgrade to High Sierra or Mojave? And where can I find those upgrades?

BTW, A bit disappointed with the Apple advice on this. There is an equivocal message partway through the upgrade that some applications may not operate as expected but this warning should have been more definitive: 32 bit apps will not operate, full stop!