SpaceX has repeatedly and reliably landed vertical stacks. On any body. Out of the engineering problems inherent to HLS, sticking the landing isn’t material because for them, for that team, it isn't as novel a problem as e.g. in-orbit refuelling or getting Raptors to relight on the Moon.
Put another way, just because SpaceX has done it doesn't mean the same problem carries the same risk for a team like IM's.
A moving barge with a known flat surface of a known hardness and stability is a whole different category of difficult than doing the same thing on naturally occurring terrain with unknown voids, hardness, roughness and consistency.
They also have the atmosphere, with drag that will make all velocities trend towards zero. Don’t have that on the moon, gotta do it all with fuel. More than half of the energy she’s by the returning falcon is aerobraking.
Yes, the moon has substantially less gravity but it’s also exponentially harder to get the fuel there.
SpaceX has landed Starship on the moon?!