Hey, had the same issue on my S20+. Visit the service centre and ask them for a free screen replacement as this is hardware related issue. They will deny at first so you have to write an email to the customer executive officer so that he can pass you...
Oh I just checked it by refreshing the software update page, it's showing OneUI 4 but I searched checkgfirm and it's OneUI 5. Thanks for the post, i would've never checked it lol
This was my first Samsung flagship and the experience is really bad! One day out of nowhere I encounter thid green line issue and now I'm pissed off about the fact that they are making us pay such an hefty amount for an issue that is hardware related...