Okay, I know this is a long shot, but here goes:
Long story short, I replaced my Q9 screen with the only compatible LCD screen available on aliexpress which turned out to be awful, so I took the risk and bought the following alleged IPS screen with the same number of pins, but nothing else seemingly compatible:
https://es.aliexpress.com/item/32869429767.html?spm=a2g0s.9042311.0.0.cc1063c0vpddyqTurns out it works! However with colour gradients the screen flickers on those areas showing such gradients. I've tried disabling HW overlays and some other solutions that google offers but I suspect it's something related to the GPD firmware not being able to correctly display colours on the IPS screen. Everything else seems to work just fine. Tried a couple of SNES games with solid colours and everything works fine.
So my question is: Is there something I could do to somehow tell the firmware to show properly on the new IPS screen? I must say I'm a total noob about FW compiling/modifying, but I can follow tips and guides