New Strange issue with touch screen 9T pro -started since December 2019


Feb 1, 2021
Hi guys,
it has been for near a month that I have a problem with the touch screen of my MI 9T pro. almost every time that want to use the phone, after touching the screen, it remains in black, and some horizontal green lines are coming to the screen. these remain on the screen for a few seconds before I can use the phone (sometimes it takes up to 10 sec ). The problem has started from the end of December. my phone never been dropped or in contact with water or any other common causes like them. I attached a short video I captured from this issue. (link for the short video I captured fro the issue: )
I recently called Xiaomi UK and someone (that I am not sure if he was an expert) advised me to not factory reset the phone and wait for a new update. The new update became available for my phone last night( MIUI Global 12.0.4) but it did not solve the issue.
my questions:
  1. is it a software issue? any idea how to solve that?
  2. Do I need to send the phone for warranty (its been a year since I bought the phone)? Do you have any experience in the warranty procedure in the UK? I bought it from a retailer-not Xiaomi.
Thanks for your help