Most React Native apps are not that hard once you get used to it.
The issue with Mattermost is that they use a lot of libraries and have a custom prebuild script.
I was hoping that the auto update could mostly work after the version we managed to publish, but it seems they often change/update their libraries so we have to investigate new scanignore rules and build errors. I am not sure it is worth it if upstream does not help.
I encounter that Mattermost Beta in the f-droid archive is more up to date (“only” 2 years old, last update: 2019-08-06) than Mattermost Classic in the f-droid main repository (3 years old, last update on 2018-04-27).
This Mattermost Beta also works with the Mattermost server of the movement mentioned in the origininal post.
I second here the wish, to keep an up to date Mattermost app on f-droid.
Would it otherwise be advised to move Mattermost Classic to the f-droid archive, if the younger Mattermost Beta has also moved and Mattermost Classic is heavily outdated and does not seem to get updates?