I am trying to revive an old Surface 3 tablet with a dead eMMC. I want to install Linux (I tried different Ubuntu variants) on a 128 GB microSD card, but it seems that Intel Cherry Trail UEFIs do not allow booting from it.
Thus, I successfully installed Ubuntu on the microSD card, with the ESP and /boot on a USB stick which I can boot from, but Grub2 only shows a prompt and the ls command only shows the USB stick partitions. I tried re-installing Grub using different live distros, also tried Super Grub2 Disk, rEFInd, toggling Secure Boot, but the result is still the same: my microSD card is not detected. However, the card is detected with installers and during live sessions.
Do you have any idea to help me?