Kip has a Samsung Galaxy S10 mobile phone, and lately, the video has become "scrambled." The image is wonky with horizontal lines after a couple of seconds of youtube. Leo says that an easy thing to try is reinstalling the YouTube app. But with an older phone like the S10 could be a bad video driver. That would require a factory reset to fix, so you want to be sure you back up your data first. Leo advises backing up with both Google and Samsung. Once you do that, then you can run the reset and reinstall the OS. Then check to see if you have the same problem. If you do, then it's a hardware issue. If it doesn't, then it was a software issue that you've fixed. From there, it's looking at your app to see if that is interfering. But if it's a hardware issue, then the only solution is to replace the phone.
You can also go to another site like Vimeo or Rumble to see if you have the same problem. If you don't, then that could point to YouTube being the problem.