Solved this on discord. Thanks for your support.
The exact reason for the problem is still unclear to me, likely an user error when updating the RTL8720 firmware.
When calling ambd_flash_tool.exe erase it prints “Flashing…” “Success!”
I am quite sure at least once i skipped the flash command as it also created the km0_km4_image2.bin files in the directory.
I thought, “oh this does not only erase but also flash the firmware”
Later I used the old version of the tool which matched an online guide better.
There I switched between revisions and while trying to nail down, it suddenly worked.
Thanks for the great support Citric (!!)