andrea did a great job summing it up here: New OS free F4Light HAL
see the wiki link in the first post.
for first time flashing, you need to put the board into dfu mode and run the respective dfu-script from the board‘s support folder. see airbot omnibus here:
rename it from .sh to .bat to run on windows machines and adjust the path to your binaries if required.
once you have it running the fw and bootloader, subsequent fw updates can be done from within MP the usual way, plus there’s a BRD parameter that can be set to opt for reboot to dfu-mode instead of reboot to bootloader.
cheers, basti.