If your Mac's macOS Catalina/Big Sur Safari browser has yet to be updated per today's https://support.apple.com/en-us/HT212816, you may wish to try forcing the browser to Version 15.0 which addresses 4 CVEs: Menu -> System Preferences... -> Software Update HTH
Updated to Safari 15 on Catalina today. After update Safari was very slow loading and surfing the net. I was getting a lot of spinning beach balls using Safari 15. I've seen complaints about this on other Mac Forums. I decided to open Safari and let the computer sit for about an hour, rebooted and Safari is now back working perfectly. Just thought I would mention this if anyone is having the same problem on Catalina with Safari 15.
I haven't had any problems with Big Sur yet. I can live with it. I like the compact tabs option. I think.
