For example, this channel is federated from Peertube as a Lemmy community. If you look at the community’s sidebar, there appears to be no moderator for the community; is this a federation issue? I would assume that the channel owner is responsible for moderation (of comments, as posts being allowed is technically a bug), but they aren’t listed.
An ActivityPub group actor defining its moderators is a specific implementation of the AP protocol. You can find the spec details lemmy uses here. An Mbin contributor recently implemented this to line up with Lemmy, but whether other fediverse software do or will is up to them, as it’s more of a community proposal than an official implementation of the spec. So when you see no moderators from other software, they likely just do not implement the linked FEP