I am curious how much work it will be to modify that Ubuntu image to fully work on the Reform. The audio chip and some other peripherals are on the mainboard, and need to be included in the device tree for the kernel to pick them up, so I would expect that at least some modifications of the image are needed.
It might already be enough to grab the device tree from the MNT gitlab, compile it, and put it in the boot partition for stuff to work. (You will likely also want to install the reform-tools - either from their gitlab or from their repository. They include a kernel module that is needed to get battery readout and to power off the laptop on shutdown.)
What helped me a lot while setting up the system was that I kept the SD card with the official (Debian Unstable) image around - every time something didn't work, I could boot it up and check how the official image does it.
At least in my case, the default OS came on an SD Card, and both, the M.2 SSD (which I had ordered together with the laptop) and the eMMC were empty. The manual contains a section about moving the OS to eMMC, so I guess that's their default setup.
(In my case there's an additional thing though: For the Banana Pi CM4 SoM the installation of u-boot into eMMC is officially not supported, as one would need a CM4 I/O board to erase it again, if anything goes wrong. I installed it there anyhow, and it's working for me, but I did buy the I/O board beforehand as a precaution.)