Hello, my name is Yvette. I've been having a problem in Photoshop that I can't explain and I hope someone here can help me with this. Please watch the attached video and please let me know if you know what's going on and how I can fix it. I actually posted this in several Photoshop Tutorial groups on Facebook, but no one offered any help.
Almost certainly GPU related as Nancy has said. Try turning off GPU acceleration in Preferences > Performance to prove that one way or another (You need to restart Photoshop for the change to come into effect). If the lines go away, then try diferent Drawing Mode settings.
Can you correlate the issue with a Photoshop update? If yes, think about rolling back a version or two, and hope that a future update fixes the issue for you.
What hardware are you using? The GPU issues with the last few Photoshop updates have mostly seen earlier video card users post to this forum with issues, but there have been some RTX20** GPUs having problems.