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.cc1063c0vpddyq
Turns 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