you can kind of tag whole communities rather than instances, for example !lemmyworld@lemmy.world which goes to https://lemmy.world/c/lemmyworld URL. It doesn’t notify anyone of being tagged though I don’t think but maybe you could tag users from a community (not sure tagging users notifies them either?)

to tag a community you type !lemmyworld in this example and then a couple choices popped up, you click one, then it changes !lemmyworld into a longer thing with brackets [ ] and parentheses ( ) like a reddit URL link markdown format