Cannot exit macOS recovery

Two days ago I connected an external backup hard drive for Time Machine and noticed that although I had 1 TB HDD, about half of it was gone. The missing half was not shown in About this mac, but in the disk utility. I tried to run First Aid and to bring the two hard disk parts together, but either the loading process simply stopped at some point or after a while a black screen appeared on the screen saying "Error has happened, please press a key or wait a few seconds". After a few attempts, I restarted the computer and pressed Command-R, repaired the hard drives from there (and noticed that the missing half was not mounted and could not be mounted), reinstalled macOS, and because that didn't work either I deleted the entire hard drive and reinstalled macOS. I erased the entire hard drive using a key in recovery mode, which stated that you should use this key if you forgot all your passwords and therefore want to start over from scratch. I used the key because all of the other keys stopped working or the computer kept crashing. Since then everything looks normal in the Disk utility, two hard disk parts with 1 TB each are displayed, Macintosh HD and Macintosh HD - Data, so as it should be. But the problem now is that I cannot reload the data from the backup in recovery mode on the computer (and I think this is partly because I had macOS big sur public beta on the computer, the software now after reinstalling macOS but macOS catalina is, and before that it said I had to use the migration assistant). And the fact that I can no longer exit the macOS recovery mode, so I cannot simply set up the computer again and transfer the data manually or log in and then use the migration assistant. I've tried everything, reinstalling macOS, completely erasing the hard drives, using an external hard drive as a startup disk, simply restarting the computer without pressing any key, nothing works.

Is there any way to leave the macOS recovery mode, e.g. via the terminal?

The computer is an iMac from 2015, iCloud is still logged in, find my mac works, macOS catalina is installed, I made a backup before deleting but the computer only shows "no system backups available" and i cannot leave the recovery mode.