Fortunately I've never been affected by screen burn but I have friends who have and appreciate how frustrating it can be as one's eyes are drawn to it.
A case of not being able to unsee it once seen ! 😒
May I ask Was the phone repaired by an authorised Samsung Service Centre ?
I ask as they will have used an official Samsung replacement display panel.
Some unauthorised engineers use 3rd party options that can sometimes be inferior and can subsequently have issues.
Just to mention … Using an unauthorised engineer will invalidate the warranty.
What I've found is that having something static for longer period showing on the display such as like widgets coupled with a longer Screen Timeout setting can cause screen burn as the icons / widgets are shown on the screen for longer keeping the pixels lit up.
Personally I have my phone set to 2 minutes timeout and the widget I use is the clock.
Really with technology advancements we are seeing on these phone's I'd expect this particular issue to lessen but unfortunately at the moment with some display panels this can still happen which is why Samsung in my experience will provide support to a phone that shows signs of screen burn as long as there's no other signs of damage i.e damage from an accidental bump or water ingress.
Current Phone > Samsung Z Fold³ 5G.