instance bans currently generally don’t federate and won’t show in the modlog of your home instance, but recent lemmy versions are automatically issuing community bans for all communities on that instance that you participated in, which allows you to at least see this in some cases indirectly.
1.0 will federate instance bans, but i haven't looked at the implementation in detail yet and i'm not sure if this is already implemented to be shown in the modlog.