Adobe won't run on High Sierra

Hi Friends, Not sure exactly how to explain this but I'll try I have an IMac 21.5-inch, Late 2013 I use it mainly for Adobe software (Premiere Pro, Illustrator, Photoshop) as well as Audacity. To this end, it's great, good screen, fast processing, USB ports etc etc However a few weeks ago, Firefox started playing up and some websites wouldn't load and wouldn't display properly so I upgraded to High Sierra (truth be told I forget what version of OSX I was running up to this point, perhaps it was Yosemite or El Cap) but apart from being unable to sync my iphone, Adobe was working fine so I hadn't bothered to update the running system (auto updates were off) Anyway, after some research I updated to Catalina and now I get the messages displayed below and I'm unable to open Adobe software (apart from Bridge and Lightroom) Obviously I'd rather have a computer with the old OSX which allows me to use the Adobe software than Catalina and functioning Firefox and websites. How do I do this? (As you can tell, I am an idiot and not the most tech literate so step by step instructions with links would be great)Hope this all makes sense. From what I've read online, Catalina doesn't supports 32 bit software, so which OSX version should I be downgrading to which will allow my Adobe software to work again? Thanks in advance for anyone able to help or advise me https://preview.redd.it/kif5u8u15h6e1.png?width=708&format=png&auto=webp&s=6fa3e0e3c56574ced2dbf1bcd2d1a8bd57f6019f https://preview.redd.it/7zip8bu15h6e1.png?width=505&format=png&auto=webp&s=7602eff43bbd3cd824e6335c3b4d799c82a30a1a https://preview.redd.it/wzan3du15h6e1.png?width=676&format=png&auto=webp&s=679b9a09a689cab002089b69af788cbbe780c07d