@Ilikecheese@lemm.ee has the right of it. @Mastengwe@lemm.ee, to search for a user not on your instance, you have search for 'username@instancedomain'. If you only search the username, it will search only in your local instance.

Edit : but when trying to tag somebody, it is able to search through other instances so maybe there is a way to implement the same technique to the search section.

Edit 2 : all my points above are for specifically how voyager behaves not how lemmyui and other clients do.