Finally!!! 
Good thing I didn’t have the time to test my homebrew way back to vanilla, this is much safer 
Edit: Worked great, had to use fastboot flashing unlock_critical (as expected, but not mentioned in the docs).
Why you would add flash_fp4_factory.sh and just have that call flash_fp4_factory.command is beyond me 
Just tell linux users to run flash_fp4_factory.command, we aren’t stupid… 