Burn-in? How common is it?

Hi! I recently acquired a Galaxy A51 (not that I needed to state the obvious) and my first thought upon learning its screen is an AMOLED display was “Oh shoot… Burn-in!”.

I just wanted to know how common it is and/or how to prevent it. I’ve never had an AMOLED display in any of my phones before. My device is second-hand. I couldn’t get much info as to for how long it was used before (although the plastic screen protector is scratched all over the place), but it seems to be working fine! At least I think so.

I’d appreciate any info you people can share. My mum’s Galaxy S9+ (which was also second hand) had burn-in after some time (she watches a lot of TikTok videos and the app’s interface was burnt into the screen) and I’d be so sad if that happened to my phone too! Thanks in advance. 💙 📱