@billster: Sorry to hear that you're experiencing issues with your Galaxy S20 FE. Are yo using a particular app or feature when the issue occurs. When you say the phone is 'cutting off', do you mean that the app you're using closes down, or does the phone reboot/shut down?
As a troubleshooting step please try restarting the phone in Safe Mode and monitoring the performance for a while, depending on the frequency of the issue. If you notice an improvement, restart the phone as you would normally and delete any third party apps you have installed, as this issue is likely to be stemming from an external source. To proceed, 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, ensure Airplane Mode is turned off.