Can you share a sample?

Sadly, it's not properly modded so there's not much we can do.

I have the S25 Ultra. It's still not out yet worldwide but I've read that it's coming soon to all One UI 7 devices.

Happen, man. If you bought your phone, first hand, check to see if it's still under warranty. You might be legible for a screen replacement

Most likely physical screen issue. You are welcome to see if it's a software issue by booting into safe mode (Tap and hold the "Power off" function until you see safe mode come on. Tap again to confirm. If there's still a white line, you most likely ...