I’m a apprentice inspector an ran across a panel yesterday and it had no main disconnect and it had the service drop supply connected to a 100 amp in line breaker to power the panel i thought this was an improper set up and looking for some feed back it also had the ground rod connected to the ground bus bar not the ground lug.
Go to your control panel and put were you are from so others may help you better.
Back fed breaker is OK but the breaker is required to be secured to the bus (usually a screw). I would comment on the GEC (looks like they cut it too short). I don’t think they’re supposed to have crimped on connectors, but not positive based on the photo.
Depends what falls under “other listed means”
Looks like a mess. Is this outdoors? If so the NM cable cannot be in a raceway. The GEC termination (lug) looks improper. The GEC is supposed to terminate on the neutral bus which is apparently does.
Call out to an electrician One side of the neutral buss isn’t even bonded to the other, differing breakers, no main hold down kit, improper GEC attachment, the list goes on.