Overall, I've noticed a speed boost in most everything on a 2019 16" MBPro (i9 processor, 32 GB RAM, 5500M 8GB video).
Unlike so many people, I LOVE the new UI changes, but then I enjoy change... it keeps things interesting. That being said, a few of the changes I don't care for - like the half-hidden folder names at the top of Finder windows. I see no point in that and it's highly inefficient.
I've only come across one tiny little utility that doesn't seem to work with BigSur - Loremify (a menubar Lorem Ipsum generator), but that app hasn't been updated in a really, really long time and I don't expect it ever will be (unfortunately). Every other app and utility seems to run just fine, for the most part. I say that because Adobe CC apps never run "just fine" on any OS, and the current versions on BigSur are no exception. Nothing earth-shattering, just annoying.
The hand-off feature that supposedly makes switching devices seamless when using AirPods doesn't work very well for me. I have an iPhone, iPad, and a Mac; wearing AirPods Pro and switching to a different device almost always requires me to manually select AirPods from the Bluetooth settings. The feature works great when it works... for me, that just isn't very often.