Hi Miles,
The graphics system in GPL was updated some time ago so that players can use modern high resolutions for racing, so when you're on the track you should be seeing something like 1920x1080. However, the GPL menus have always been limited to the old SVGA resolution of 640x480. Most modern monitors can 'upscale' the menus to fill the full screen, and most manage to do it with better quality than you're getting.
Please check the settings on your monitor (not the GPL settings or windows settings) to see if you have something which says "upscaling" or "resizing", and try changing it to a different setting. I think that might solve your problem.
Alternatively, the FXAA anti-aliasing settings in Windows have been known to make GPL screens look messy, as John says above.
I'm afraid I can't be more specific about the details as I've never had this problem myself, I just remember what others have spoken about in the past. If anyone is more familiar with those monitor settings, feel free to add to my information. Good luck finding a fix, and welcome to GPL!
Edited by Saiph, Mar 21 2019 - 02:07 PM.