What does happen?
As stated in this Thread it should be possible to boot from MicroSD.
I tried it today, since I wanted to restore a Backup to my internal V SSD, but it was not possible to boot from the rescue Drive I created on an 8GB MicroSD Card using the built-in MicroSD Slot. Actually there was no Option to boot from the SD Card Reader in the UEFI.
I am pretty confident the SD Card was not the problem since it was possible to boot from it using my Aukey CB-C55.
What should happen?
The MicroSD Slot should be choosable in the UEFI to be able to boot from it.
How can we reproduce this issue?
Create a bootable MicroSD Card and try to boot from it with the Slot below the Kickstand. Try to boot from it using a USB Adapter to verify it is not the SD Card.
Full Description of what I did
I used Paragon Partition Manager 15 with this fix to be able to create a WinPE Boot Media.
Furthermore, I added all the Drivers needed for the SSD and the Network Adapter (from the Aukey Adapter) and the Devices which the two Devices are connected to in Device Manager. (But I do not know if this step is necessary!)