no, and i don’t think you can actually use it for direct sideloading - I just duplicated the format @k4y0z used in his images. Only content are the partitions (format <partition_name>.img ) that are included in every OTA update, which are dumped from the phone. I dumped them like this (example for slot A):
fastboot boot twrp.img adb shell $ cat /dev/block/by-name/system_a >/external_sd/system.img
for each partition name in slot a, then i got the images down with adb pull
the metadata I added by analogy by copying info from the one in the differential update for the same version, I don’t know if that’s good for anything.
then just zip it all together with maximum compression
the list of partitions I simply used the same set that the FP OTA update updates (payload_updater in fakediff mode will list them)