I don’t have an account on lemmy.world but it still shows up in a separate section for viewing posts and on the search page.
Does the app assume users to have accounts on lemmy.world?
You can go to the account settings, long tap on Lemmy.world and remove that instance, or you can do the same to remove any other instance.
You can still interact with and view posts from lemmy.world, even if you don’t have an account there, that’s part of the whole federation functionality.
Is it that you don’t want to engage with that instance?
You can view them, but you can’t interact with them. When I try to upvote a post or comment when lemmy.world is selected I get an error message along the lines of “This thread was retrieved via lemmy.world. You are not logged in.” Forgetting and then having to search the post on your own instance to interact with it can be a bit annoying.
Edit: I just saw that they added an option to switch instances when viewing a community in the latest version. Great news!