that likely means your instance hasn't federated with lemm.ee or has it blocked, check the block list and if its not blocked search the text "!osr@lemm.ee" in your community search, it will show not found but if you leave it a second to index it and try again it should work

IMO it goes triply so for games with guns, if regular enemies can just shrug off bullets to the head I have difficulty enjoying it cause it just makes the weapons feel weak