I have bought an App by the name of Fantastical. The cost for a year is just under $40.00. It does what Apple Calendar Notifications should do, and did do in Catalina, but doesn't in Big Sur.
Fantastical has snooze options a plenty, more than we had in the Apple native calendar in Catalina. It looks pretty much like the native calendar You will need to connect it to Icloud. Fantastical gives you instructions how to do that. And you need to change the native calendar notifications in system preferences/notifications to "none".
Of course I continue to hope to see the Apple engineers pay attention to this stupid mistake. If I don't don't get too hooked on Fantastical I will revert to the native calendar if Apple wakes up. $40.00 for a year to get rid of an annoying headache seems cheap to me. My doctor charges more than that to treat a headache.
This is not the only "pain" Big Sur has visited on me..It also is not playing nice with the print option in Chrome on one of my printers.
No wonder so many smart and tech savvy folks do not update when Apple tells you to do so.!!!!!!!
[Edited by Moderator]