Weird line on screen ? unsure what it is.

Hello, does anyone know what this line is in the top right corner? or what it possibly could be & how to fix it?? it started out thin but it is getting worse it seems. I don't really drop my phone & i use a screen protector. In the photo I took of the screen protector. There also has not been any water damage that i’m aware of. Never dropped it in water or any of that so im not sure what caused this. It just showed up one day. I’ve tried turning my on and off but still remains. This is an iphone xr and ive had it for almost 4 years now. I really do not want a new phone right now because I cannot afford so i’m hoping it can be fixed. Thank you.