I downloaded u-boot from your git (yes i used that link) and installed u-boot via pacman. Then i dd'ed u-boot.kpart to mmcblk0p6. I created the extlinux.conf file by copying it from my RockPro64 board and changed append to match that from vman's post on page 11
The
scary boot screen shows its normal "press space to disable developer mode", but i think you meant how it looked past that point (where it should show u-boot).
I looked like Star Wars in fast-forward without color
I mean black ground and white pixels got refreshed than half the screen with white pixels, then refereshed to only black and than from beginning. I think the machine tried and tried again to bring u-boot up
I succsefully setup a bootable usb-stick yesterday with which i reflashed linux kernel on KERN-C.
Your script does install the same package (and u-boot) i got on mmcblk0p6 and on mmcblk1p1 before i flashed a kali image on it, so i dont think it will give an other result, but if you want i'll try again with your script.
Thanks for the hint about downgrading mesa