Disable subtitles and see if it still occurs
If this is an "app"......i'd suggest re-installing it.
if this still happens, then it's a glitch w/ the app and the tv's software. have you updated the tv itself recently?
I had the exact same TV, I would frequently get those lines in YouTube. Never found out why it was happening, but a reboot generally fixed it temporarily for me.
Had the same issue. Rebooted the TV resolved the issue. I had taken a video and called in support. They sent a technician and replaced the main board.
Does your TV support local dimming?
I looked it up it does. Do you have it turned on?
change the color of your subtitles. you can do this while you play a video - go to subtitles. same for netflix
I get that with Prime video on Firestick 4k and subtitles. I'm using 7th generation Samsung TV, it happens on both TVs and they are both TU7000 Samsung TVs.
It's you HDMI cable.
Can’t help with the pixel lines, but Reacher is awesome.
Looks like some kind of electrical interference. A Universal Power Supply would filter it out.
Since it's an Android TV, install a diagnostics application. That way you can test the pixels, backlight, refresh rate and response time.
It's s possible to be software related, it looks like screen tearing due to the frames not syncing correctly with the display refresh rate.
It seems weird to me that the artifacts only appear on the subtitles part. I know some streaming services burn in the subtitles when transcoding, before streaming to the client. You can try to override the built-in subtitle settings with your TV subtitles settings through the accessibility menu.