My understanding is that a Lemmy Instance Admin has control over Users and Communities originating on their Instance, and can (in extreme circumstances) defederate from another Instance, so that Users and Communities from that Instance are not visible to their Instance’s Users.

An individual Lemmy User can block a specific User or Community, but not yet an Instance (though that feature appears to be planned.)

Therefore you might want to simply block the offensive User or Community.

If you feel strongly about reporting, then you should contact the Admin of the Instance hosting the Community.

If your report isn’t resolved to your satisfaction then you may want to escalate to the Admin of your Instance to inquire about blocking the Community for all Users on your Instance, or even defederating from the offending Instance (though this is the “nuclear option” as it would affect ALL Communities and Users from that Instance.)

tl;dr You have the power to block Communities you don’t like. That option is found in the Sidebar.

Edited to include @Earthwormjim91@lemmy.world’s option.