Had same issue, copied files to external drive.

This morning I was given the Big Sur upgrade notification. I was a little worried but after a TimeMachine Backup gave it a try. Install took a bit longer than mentioned on the screen. Machine rebooted and gave the Apple logo with progress bar. After that it rebooted again and now it looks stuck at about 30% progress with mouse pointer. It is like this for about an hour now on my 13" Macbook Air 1.6GHz (2017?) Should I wait a bit longer or go for the reset? I'm coming from Catalina. John