Should I upgrade to Mojave or Catalina? on iMac Retina 5K, 27" Late 2014, 16 GB RAM

I have an iMac Retina 5K, 27" Late 2014, 16 GB RAM. I am still running El Capitan 10.11.16 and have not updated for host of reasons (mostly old Adobe software and iPhotos mapping capabilities). I have to finally upgrade for email and browsing compatibility due to Let’s Encrypt's Root certificate expiring late September 2021 and Gmail changes last week. Should I upgrade to Mojave or Catalina? Is Mojave enough to avert Root Certificate expiration issues?

I use the Adobe Creative Suite CC so worried Catalina requires 4 GB of RAM, twice as much as Mojave and what I use now.

Also 32-bit vs. 64-bit issues: Apple Support just said (after looking it up) that High Sierra was last OS to be 32-bit. Is this correct??? Everything I read says Mojave is still 32-bit and Catalina is first 64-bit OS so that is a major concern. Am assuming I have to check all old apps to see if they are 32 bit? Are old fonts, mostly Open Type format but sometimes Postscript affected by 64-bit?

A friend with a 2015 iMac just upgraded from El Capitan to Catalina and said it bricked his machine and it was a nightmare getting it back, think he finally got it back from Time Machine. Elsewhere I read of sometimes Time Machine not working as a restore btw. I've never tested mine.Have others had this problem?

If I got to Catalina, can I still use/restore from Mac OS Extended (Journaled) external drives that host my current Time Machine and other back-ups?

Just wondering advantages of each and what various trade-offs might be. Do people like Catalina?

Thanks for all the good advice so far....