I think first you should join a number of communities you are interested in @fiveboringgames. I’ve subscribed to quite a few.

In order to cross post you have to be a member of that community.

First do your post in whatever community you want and post it.

Then go to the post after it is published and edit it (three dots on lower left hand side). The edit will show you a list of things you can do. One of the things is cross post.

When you click the cross post option a screen will come up and ask where you want it to go. When you start to type all your communities you joined will show all your communities and you just click on the one you want to cross post to. Then finish off.

I’m just doing this from memory so hopefully I’ve included everything.