Big Sur installation restarts at 12 minutes left mark

[sortedcord]

Well this is technically a non-issue you can simply ignore it and when the laptop reboots, boot into the install macintosh entry not the one that says "(External)".
After doing this u might see that the installation goes on for 30 minutes or so until it suddenly reboots again. Don't panic, just keep moving along that and boot into Install Macintosh again. You might have to do this for 2 or 3 times more until you see the final setup screen.