Haven't seen this myself, or heard of anyone else with the issue. When you say flickering, do you mean high frequency on-off or significant brightness change, or more slow?
If we are talking about high frequency flicker, the genius bar is your best bet.
If it's a more slow transition, could it be (and yes I know that i'm likely telling you to suck eggs, apologies) that auto-brightness (or true tone / night shift) are doing something odd. I ask because I've noticed that when reading with a bright light behind me, my iPad is very sensitive to where my hands are on the device and as a result the screen brightness can vary quite a bit.
I'd try these things just for giggles
/Settings/Display & Brightness/Auto-Brightness disable and test
/Settings/Display & Brightness/True Tone disable and test
/Settings/Display & Brightness/Night Shift disable and test
Also what happens in a totally dark room?
Hope this is somehow helpful & good luck.