S21fe lags alot and settings not working

This is my father's phone, i checked for permission to install apps and only WhatsApp had access to it. Following action taken by me:-

1. Although now i have disabled it, the settings simply crashes.

2. I have also installed malwarebytes and it says no malware found.

3.tried to safe boot but that just loops to "samsung" default loading image and never safe boots.

The phone is lagging alot and my father denies installing anything in the phone. What other steps do you recommend?