Is my Mac compatible with Big Sur?
If Apple lists a device as 'supported' by an OS, then there should be no problems running it. (In fact, the reason that older Macs are excluded from newer OSes can be that the OS performance is not within Apple's expectations.)
I run Big Sur on a 2014 15&quot; MacBook Pro, which functions very well.
I would suggest that past performance issues are likely to be caused by incompatible software that needs to be updated, or things that are incidental to the OS update.