Same here. MBP 2020 2GHz, quad i5, 16GB RAM. Immediately noticed the difference as soon as I upgraded to Big Sur in terms of "laggy" behaviour during general usage of the laptop. Resizing windows, typing, scrolling in safari, moving between desktops...basically everything. Was actually super content with the previous Catalina version, no gimmicks, no drama, no complaints about the OS since everything worked buttery smooth...I should've waited for the updated Big Sur version so that all these teething stages of new OS updates (especially for ones with massive overhaul such as Big Sur) get sorted out :(( For me it's definitely an OS issue (I hope, and it better be), I only bought this damn machine just over a month ago! NOTE TO SELF: always wait for the version 2 of new tech /OS.