Yesterday, I tried to access the forum from the app, but it wasn't possible. I suggest trying to add this feature to make lichess even better.
While I understand that adding a forum is a lot of work, I think it would be easy and useful to add "go to lichess website" button in the android app.
When you follow a link to the forum and select "open with lichess app", it already opens it in a web browser, so functionality is there. Would be nice to have this option from within the app too.