Experiences with self-hosted community apps with mobile app front end

I'll be starting a new non-profit project with an upcoming-but-not-imminent need for a community/discussion platform for groups of volunteers and service users.

I'm looking around for a battle-tested, self-hosted server app to facilitate community discussion that can be accessed using a smartphone app, ideally with no or minimal licensing fees. The project I am currently working with uses the Disciple[1] platform, but that's prohibitively expensive and has questionable reliability.

I am considering Discourse at the server side, with a third-party mobile app for the users, but I am interested in any feedback or advice as to other solutions that might be worth looking at. I am comfortable self-hosting, and I am open to new or established technologies.

Thank you.

[1] https://www.disciple.community