It's not app specific - that's just how the Lemmy code works at the moment.

For this specific reason, Lemmy integrated search feature is fundamentally broken at the moment, so you should be using https://lemmyverse.net/

When I first joined my instance I couldn't see any Xbox communities so I created one. It got a little following, but then I found out there were already two communities literally called Xbox but no one from my instance joined before, so I couldn't see them.

It has to do with how federation works. There's no federated broadcast to all instances in the threadiverse when a community is created. Each instance has to be taught about each community via a search. I think this was done to prevent broadcast storms due to community creation, though in normal circumstances community creation is not a high frequency activity. I think the world would be better off if community creation broadcast but was rate limited.

At any rate, in the meantime search for communities at lemmyverse.net. It's way WAY better than the native community browser. Then just use the native community browser to find an sub the specific thing you found in lemmyverse.

This is not the way. Remember, most if not all instances are non for profit. If you force an instance to host all of the federated lemmy content even content nobody on that instance is subscribed to it will have a financial cost that I think no admin is willing to pay. Also admins will soon be purging data that is not being subscribed to by the users of that instance, so it will just be a waste of time, and might even get you banned from that instance.

After i visit community on another instance and it shows up searching from my instance, do i or someone else on my instace need to join on that community for it to show on my all communities feed?