UPDATE and found my personal solution after half a year... Now, on Big Sur 11.4, in July 2021, I was still annoyed by some level of choppiness of the UI, especially while running on the Intel GPU. For example, I had noticeable lags while typing in Pages, as if this great Laptop was seriously to slow to process simple word processing. Don't get me wrong, everything usable in a decent way, but with micro stutters and little hiccups on a regular basis. On top of that, battery drained 50% in 2,5 hours working in Pages with some background Apple Music running, nothing fancy - to much for my nerves, knowing I spend 3,5 grand for this machine not even a year ago ... So I looked into it, and found out that the screen saver was taking some amount of CPU-time. Not much, like 3-5 % of total CPU. This, of course, without it being active, because I was using the system. I had this switched on all the time because I use remote access from an iPad often, and sometimes the system would have long idle times. So, I decided to switch the screen saver off to test this out and guess what - my MacBook Pro 16 inch went instantly back to snappy UI handling. No issues anymore with Safari browsing, typing in Pages and so on. Felt like o.g. Catalina for me, especially on Intel GPU. Finally. Long story short, give it a try - switch screen saver off. Worked for me.