Like there is a dedicated discord forum for community, snaps etc. Have you considered opening one for flutter? It would be a good place to coordinate between devs, community, learners, discussing issue s etc.
You can find links to a number of community resources here:
In particular, there is a Google Groups mailing list (which you can interact with through a web browser if you prefer) and a sub-reddit. I don’t think any of it is built on top of Discourse though.
These are saturated with devs on other platforms, there is no community for Flutter on Ubuntu.