This feature was dropped in one ui 7. Sad to see that its the same in one ui 8

Yes it happens with all phones in general, atleast all samsung phones...

Please take your device to a service centre, maybe they will be able to help

My S21FE is working the same as it was on OneUI 6.1, I am facing no issues that you have mentioned, yes the phone gets slower now but I think that will be fixed in OneUI 8, as I had noticed that phone was laggy in OneUI 6.0 but that was fixed in 6.1