@chillybons: Please try restarting your Galaxy S21 in Safe mode, as this will disable all third party apps, and help to determine if the issue 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.
With Safe mode enabled, monitor the performance for a few hours, depending on the frequency of the freezes/restarts. If you notice an improvement, restart the phone as you would normally and uninstall any apps that you have added since you first encountered the issue. Let me know if this helps.