Most of the fediverse client apps only support the Mastodon API. That doesn't really work for us, because we're not even remotely like Mastodon or Twitter.
Just visit your site on a mobile web browser and from the browser menu bar "install app". It's called a "PWA" or Progressive Web App. I did get a warning on the most recent Android update that our app wasn't compatible with bleeding edge Android, but everything still works. I'll just need to figure out what they changed to get rid of the warning. It only showed up once. Push notifications are still in progress, but there's only one of me and have some other priorities and need to get back to that task as soon as the current one completes.