It will only show up on other instances when a user there searches for it manually.
Lemmy Support
Support / questions about Lemmy.
At least one person on each instance needs to search for it. (While logged in) This will make the instance "discover" your community.
They can either take the full url, https://lemmy.ml/c/skypictures or !skypictures@lemmy.ml and paste it in their instance's search bar.
They're working on making this a bit more automatic but for now that's how it is.
Some feedback to see if this is similar for others. First I tried searching 'skypictures' and only this post came up. Then I tried '!skypictures@lemmy.ml' and got nothing. Lastly I tried 'sky pictures' and it appeared, but with only one post instead of two.
It seems like a hit or miss. Also, some instances take a while to sync all the posts and comments.
I really hope devs fix this.