This repo contains the fixed DSDT tables for GPD P2 Max for it to function correctly under Linux.
Note that the fixes are not specific to Linux. It works fine in Windows simply because the Windows driver does not care about the DSDT definitions as much as the Linux one does. The DSDT itself is broken in its stock state.
You can consult ArchWiki#DSDT for instructions on how to use it. Basically you need to re-compile the DSDT file, package it into a CPIO archive, and append it to your kernel's initrd option.
You can find a pre-built CPIO image named acpi_override in the GitHub Release page. Download it and copy to your /boot partition, then add something like
initrd /acpi_override
to your bootloader's configuration. Don't replace the exisiting initrd options, just insert it before your original initrd option.