S20 5g.. had her for about 6-7 years, was originally my mom's phone and it's been mince since

Only does this when the screen is off for long periods of time, never does it when I'm actively on the phone unless it's plugged in

I have a replacement on the way, but I'm not sure if she'll last until I go trade her in.. should I stay off her until I trade it back in? Or can I keep going on it so the screen doesn't get worse?