@laurarobo: Please can you try heading to Settings > Battery and device care > Tap the 3 dots in the top right > Automation, and check to see if 'Auto restart at set times' is enabled? If it isn't, please can you confirm if you're able to power the S22 back on when it switches off, and if the device has sufficient charge when the issue occurs? You can also try restarting the phone in Safe Mode, as this will disable all third party apps, and help to determine if the problem is stemming from an external source.
To enter Safe Mode, press and hold the Power button until the 'Power off' prompt appears on the screen then release > Touch and hold Power off until the 'Safe mode' prompt appears then release > To confirm, tap Safe mode. Monitor the performance for up to 24 hours, depending on the frequency of the restarts, and if you notice an improvement then please restart the phone as you would normally and uninstall any recently added apps.
