apple watch 5 and bug surf don't work, i'm unable to unlock mac with watch ...

Same issue here (Apple Watch series 6, Mac mini 2018, iPhone Xr).

I have tried all the workarounds mentioned in older forum posts, but none have been successful. It's not a dealbreaker, but I hope that a quick bugfix release is in the works.

Same issue for me (Apple Watch 6, MacBook Pro 2018). Deleting the key chain entries did not work. However, signing out with my Apple ID from my MacBook Pro and signing in again, then restarting helped.

Thank you DRCDIETZ, it worked for me too.

I have an other issue with Big Sur: in my desktop, the alias icons (linked with a NAS in my network) don't appear with the right icons. Have you the some issue?

Thank you

Thanks DRCDIETZ - worked here also.

Perhaps Apple should implement a re-auth / re-login into iCloud for each major and point releases of it's OS's. More and more is tied into that cloud service, and honestly not all of it's dependencies makes 100% sense.

Apple Watch 6 does the same thing. Get message "Your Mac was unable to communicate with your Apple Watch." restarted both 2019 iMac and series 6 watch. Very annoying and a big waste of time. Doesn't anybody in the Big Sur test team have an Apple watch?

Don't works with Apple Watch 6 too.

Please Apple fix it!