It would be much more convenient to have a thread have all the comments that are on crossposts and threads with the same link. They could have a little indicator mentioning the title of the thread it’s posted on with a link to the thread. This would also help people come across new communties.

It could look something like this

clicking on the link to the thread could open it within the app allowing you to then easily browse the community in case you want to subscribe to it