There's a truly excellent, open-source Mastodon client called Ice Cubes which hit the App Store yesterday. The very first thing I did was donate the maximum possible IAP.
(I wish the FediActivityPub people had spec'd up an API to avoid this kind of multi-implementation-who-supports-what shambles.)
EDIT: Amusingly, I fixed the "cannot login to Pleroma" problem for `madon` this week - Pleroma/Akkoma require form data in the body, not the URL, for POST requests (which is fair since the HTML spec suggests this is the Right Way.)