moddien

@moddien Why did you try to burn the image in the eMMC without being sure it would have worked?
If you can boot multitool again, clean the eMMC and start fresh.
 
I have prepared an armbian bookworm image with opensource optee in place of the proprietary one, you can download from here; I have not tested it at all, so can't guarantee it works.
If you want to try it, first clean the eMMC with multitool and then try to run the image from an sdcard to see the outcome.
 
 

Two same boards but different cpu.
Rockchip labeled works fine with armbian, multitool and libreelec.
The board with huawei labeled cpu has the previously described problem, multitool and armbian stop working after a minute.
Method of switching bootloaders suggested by @jock  works.

@moddien thanks for the firmware, I will try to inspect as soon as possible.
Usually the first page of the thread and the last 3/4 pages are enough to get up to date with recent developments.
Many useful experiences are scattered through the  thread, but usually the most important things are collected in the first page.