Hi, @timotheus 
I've never used a GPD device, but from what I've been searching, I think the easier solution for you is pretty similar to the one that @John1 wrote for installing Ubuntu MATE 22.04 in the "GPD Pocket 3" in the following answer, also here in the "Ubuntu MATE Community":
By that, I mean that you probably should, for the GPD MicroPC, do the following:
1 - Download the regular x64 Ubuntu Mate 22.04 LTS ISO - "ubuntu-mate-22.04.1-desktop-amd64.iso" - file (or newer "point release", when it becomes available) from the "Choose a download | Download" - https://ubuntu-mate.org/download/amd64/jammy/ - web page to your "regular" computer.
2 - Use that ISO to install Ubuntu MATE on your GPD MicroPC computer/device
3 - Then run the following commands:
git clone https://github.com/wimpysworld/umpc-ubuntu.git
cd umpc-ubuntu
4 - Edit the umpc-ubuntu.sh file (located in that "umpc-ubuntu" directory) and change UMPC="gpd-pocket3" at the top of the script to UMPC="gpd-micropc"
5 - Run the script to enable the configuration tweaks.
sudo ./umpc-ubuntu.sh enable
An ALTERNATIVE solution would be for you to create an ISO with the customized hardware tweaks and then use that "custom ISO" to do the installation, by doing the following:
1 - Download the "normal" AMD64 ISO - "ubuntu-mate-22.04.1-desktop-amd64.iso" - file (or newer "point release", when it becomes available) from the "Choose a download | Download" - https://ubuntu-mate.org/download/amd64/jammy/ - web page to your "regular" computer.
2 - Run the following commands:
git clone https://github.com/wimpysworld/umpc-ubuntu.git
cd umpc-ubuntu
3 - Run the following command to create an ISO with the customized hardware tweaks for the GPD MicroPC:
sudo ./umpc-ubuntu-respin.sh -d gpd-micropc ubuntu-mate-22.04.1-desktop-amd64.iso
4 - Use the customized ISO to Install Ubuntu MATE in your GPD MicroPC
References:
In that last page - GitHub - wimpysworld/umpc-ubuntu: Scripts for UMPCs such as GPD Pocket, Pocket 2, MicroPC & TopJoy Falcon - the section named "The Scripts" is of particular interest.
I hope this helps