Thanks for replying! Well, it's my first time posting here so something had to be lacking 😛
I'll be more thorough next time.
So, I'm already using the latest version of Foxit Reader, installed Adobe Reader and the results are the same.
Uninstalled Foxit Reader and Adobe Reader and it defaulted back to Edge.
Same results.
I think that the PDF files are the likely culprits, because some of them don't display those lines while others do.
My NVIDIA RTX 3070 still has drivers from May because the releases have been so unstable that I can't constantly replace the drivers.
But it's the first time I'm experiencing this... I don't know. I'll look for a solution later.