I have had the Fold³ since release.
The internal factory fitted screen protector delaminated so I peeled it off.
Replacements can be purchased from places like Whitestone Dome etc or one can ask Samsung to refit a new one.
I use mine without one now.
The ' crease ' itself has not had any deterioration at all.
The crease is created by the way the phone folds so is part of the manufacturering.
The display itself is a softer material to allow the folding of the phone.
You cannot fit a secondary screen protector over the factory fitted one. It would probably affect the sensitivity of the touch screen.
I wouldn't contemplate removing the original one unless delamination occurs.
I'm very happy with my phone albeit its the Fold and not the Flip.
I have colleagues at work who have the Flip³ and Flip⁴ and there very happy with the phone.
I hope that also helps in conjunction with the excellent advice from @Glenntech 👍
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "