Now that I've become a user, my iMac crashes about once every 3-4 hours. How can I prevent this?

I'm running on macOS Catalina 10.15.7. The screen and cursor freeze, forcing me to do a manual shut-off. After re-starting, the cursor is still frozen, requiring a second shut-off. The pattern is always the same. Happens approximately every 3-4 hours of use.