I guess I just bricked my GT1 by uploading wrong firmware. Which is the correct one for me (S912BKLG90736 16GB)?
And why is there no search function????
Yep. Using TWRP noticed that eMMC was 0GB (hence broken) --> unit scrapped (no help from Beelink replacing eMMC's). Just bought a GT1 Ultimate (re-used); Ethernet not working but rest OK :-)