iPhone screen turns grainy/noisy

i’m a little disappointed with apple. i’ve had iphones since many years ago and have never really had any issues with the software or hardware.

may 2021, my iphone 12 Face ID is stopped working, as well as the portrait selfie camera. tried all resets and restoring my phone and none worked. so i brought it to a local apple service provider to get checked, and finally, i have to claim my warranty for an iphone that i have only been using for two weeks. they said that i will probably get a replacement with a new unit.

after two months of waiting (may 15-july 19), the new unit has arrived. everything was fine at first, but a few minutes later, my screen suddenly just turns grainy like there is a noise in a grainy night photo. i talked to the technician, and they recommend that i update iOS and try all resets, but nothing changed. so they offer me a solution that i have to reclaim it and i have to wait again for another week(s).

is there anyone who experienced the same issue?