Do you know what the backup consisted of?...Did you read the screen ?
It is possible that there was a kernel update, because you rebooted after the update finished.
If this was the case, do you see the grub screen prior to logging in ?.....it will be a list of the available kernels which are stored on your pc.
If you do see that screen, hit the down arrow when it appears....that will stop it proceeding further.
Arrow down to the kernels below the two which were installed via your update....they should have the numbers 5.4.0-105 & 5.13.0-37
Choose the first generic kernel below those...probably 5.4.0-104
Hit enter
The pc will boot to that kernel
Success?