Xiaomi screen flashing issue

Hello everyone!

I changed my phone a month ago to a Xiaomi Mi 9T and everything was fine until about two weeks ago when my screen started to flicker with big white flashes (rapid alternation between black screen and fully white screen at maximum brightness) every time I turned it on.
At first, it wasn't bothersome, I just had to deal with a couple of flashes (waking up to that is still not very pleasant haha) and my screen would light up, but gradually, once the flashes started, they didn't allow for my normal screen anymore and the only way to make them stop so I could access my phone was either to spam the power button or to restart it.
This technique worked well but of course it didn't last; I then had to restart it multiple times, sometimes it only took 30 seconds, other times it took me 10 minutes to get it to work.
And all of that until this morning when, no matter what I do, the flashes won't stop, and it's impossible for me to use my phone because of them, even after restarting it an infinite number of times.

In the meantime, of course, I tried to solve the problem but no matter what options I changed or what brightness levels I set, the flashes consistently returned.
I searched a lot on various forums but I've never encountered a problem like mine...

So I'm calling for your help; at this point, I don't know what to do anymore, I don't even know where the problem comes from or if the warranty could work on this...

Thank you so much for taking the time to read and for any potential responses!!
I wish you all a great day!