I want to downgrade my mac

Hi Megan , to do a downgrade from newer macOS to old macOS isn’t easy because many things that you are using from macOS Big Sur won’t work with macOS High Sierra , plus the entire HDD needs to be erase and you will lose everything you have stored in the hdd except thd iCloud services, are you aware of that ?

Ozzie is correct, but you better get an external drive to backup to ASAP!

Which Apps aren't working?

definitely I highly recommend you stay on macOS Big Sur ,, check every app that is not login at start up the Mac and safari extensions and music games movies are not playing in background, if your Mac is compatible with macOS Monterey just try to get the update if not so macOS Big Sur still is on 11.6.3 so very soon will be in 11.6.4 there is a new update on the way, my iMac use to runs slow but I delete a lot of stuff that I do not need like numbers, pages apps and others apps that I do not use and now my iMac runs flawlessly

Thanks man for backing me up.. usually people when installing an app let them running in background when the Mac starts up and Safari extension is another pain in the neck

Keep up the great work my friend. :)