I think the way it runs on ONDA is more hacky and complicated than it probably needs to be for Medion, if it's based on same device tree. Onda has 32-bit UEFI firmware and no kernel source code available from vendor, so basically I adapted Jolla Tablet kernel tree for it and used GRUB2 bootloader to boot 64-bit kernel with 32-bit UEFI (32-bit kernel can be also used in theory, but there is weird bug with kernel panic on starting PulseAudio). Since Medion is Germany-based, can you request GPL kernel source code from them? It's either not present on their website or I couldn't find it.