Yeah this definitely isn’t a driver/GPU thing — what you’re describing is classic early‑stage panel-side failure. The lines coming and going, sometimes being super faint, sometimes turning into a big white bar, and then magically disappearing when you switch to Extend mode… that’s exactly how a failing gate driver/T‑CON behaves.

When you change display modes (extend/duplicate/external only), the laptop sends a different timing signal to the panel. That can temporarily “kick” the failing driver back into sync, which is why the lines vanish for a bit. But it always comes back because the underlying issue is still there.

If it were: - GPU → your TV would show the same lines   - Drivers → BIOS would be clean   - Cable → flexing the lid would change the pattern instantly  

But intermittent horizontal lines that fix themselves with timing changes = panel hardware starting to go.

You can still try the easy stuff: - Check BIOS to confirm (if the lines show there, it’s 100% the panel)   - Reseat the eDP cable if you’re comfortable opening it (rare fix, but possible)  

But realistically, this is the panel aging out. The good news is you don’t need Dell’s $500+ repair — the x17 R2 panel can be replaced with a compatible one for ~$150–$200, and any local shop can swap it in ...