The marks your seeing might be the degradation of the oleophobic coating on the display that helps to repel fingerprint marks etc.
Normal wear and tear over time means this can start to degrade.
Your fingernails simply are not strong or sharp enough or made of the material that would scratch the screen my friend.
You could look at fitting a screen protector that may hide the marks if they are always catching your attention.
If I can be of any further help then please don't hesitate. Take care. 😎
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. "