After updating my Mac Book Air to Big Sur, I have not been able to log in to my iCloud account, iMessage and FaceTime.

I purchased my brother's old Mac Book Air and restored it to new and set it up, but it would not let me set it up on Big Sur, so I had it set up on a previous version. I got an update for the laptop to Big Sur, so I did the update and now I am not able to log into my iCloud, iMessage or Facetime. I have updated my password and that is not the issue because I am getting a message that there is an unknown error.

Thanks,

Thelma