Booting Xiaomi Mi Box S 2nd Gen

I’m trying to get Corelec installed on Xiaomi Mi Box S 2nd Gen.
It is an S905X4 SOC. It doesn’t have onboard ethernet, but connecting one via USB-to-Ethernet works for gigabit.
I’ve tried both variants of the S905X4 SOC in the installation guide, both fail to boot.
I used ADB and got to the boot menu, I was able to select “install update from Udisk” or “install update from SD card”. Udisk worked (shows the file selector), but it’s not a boot sequence.
Does this device even support dual booting?
I saw this tutorial on how to root the device, but I have no idea what to do afterwards and if there’s a way to revert the changes to factory specs.

I also now updated the device to unlock the bootloader based on step 5 in this tutorial:

Still, upon boot from external USB drive, it seems to just reboot again and get back to Google TV UI.

What do you get when you run fastboot command: “/path/to/fastboot getvar all” ?

This is not only wrong topic but also wrong forum. Ask your related questions on Android forum.