M1 iMac not backing up to AirPort Time Capsule.

You have already performed basic troubleshooting steps like.........

Powering off the Time Capsule and leaving it off for a few minutes

Restarting the M1 Mac

Powering up the Time Capsule again

Is that correct?

If you have already performed the power down and power up checks that were suggested........and the M1 Mac is still not backing up to the Time Capsule.........I'm not sure why you marked that check as the solution to your issue.

If the M1 Mac is still not backing up, the next checks to perform would be.........

Hold down the option key on your M1 Mac while you click on the Time Machine "clock" icon at the top of the screen

Select Verify Backups

Let the process run until it completes or until you see another error message. The process might take anywhere from a few minutes to an hour or more depending on how much data is backed up on the Time Capsule.

You can watch the process by clicking on the Time Machine "clock" icon again and then clicking on Open Time Machine Preferences.

Post back when the process has completed or if you see an error message. If an error message appears, post back with the exact text of the message please.