Apple Watch cannot open Mac and/or Sidecar doesn't work over WiFi

I had trouble with unlocking with apple watch after the upgrade - the same "watch not communicating.." message. I unpaired and re-paired the watch and rebooted which fixed it. Then I installed avira anti-virus and once again the watch wouldn’t unlock so I uninstalled the anti-virus and the watch worked again. Does anybody know an AV app which will work with apple watch unlocking?

Yes, sign out and sign in the Apple ID again can solve the problem.

My Apple Watch is unable to unlock my Mac after upgrading the MacBook to macOS Big Sur. The system always said "Cannot communicate with apple watch"

I also delete all of the "Auto Unlock" items on my iCloud Keychain.

Hi I fix it Apple Watch unlock the Mac whith sign out Apple ID on my Mac , reboot and then sign in whith Apple ID , sidecar stay issue : (

I signed out of the iMac and MacBook Pro, rebooted, then signed back in. This forced me to sign back into all devices. But it worked.

The unpairing of the watch, then pairing it again totally worked. Thanks everybody!

Worked like a charm...cheers :)

This has FINALLy fixed the issue!!! WOW I am HAPPY!!!

This solved my problem. Thanks!

This worked. Thanks!

Works the charm, many thanks for the suggestion.

Thanks so much, this was frustrating me no end. This fixed it straight away.

Worked perfectly! Thanks!

Now I have log out Apple ID on my iPad and then reboot iPad.At the first log in on iPad I log in on my Apple ID and and handoff working but sidecar just see my iPad before nothing see it , but when I try to connect on iPad give me an error message "the device waiting time has expired". What? bla bla .... It doesn't make sense, to me it's a bug of Big Sur

Just uploaded to Big Sur on my Mac. Have the Apple Watch 6. Coming home with Big Sur starting, my watch is not communicating with the computer anymore. People here have said sign out of your AppleID and then back on & it should fix. How do you do that?

Thank you!