@kirschwipfel for IOS/MacOS SiskinIM and BeagleIM works best for me.
For IOS there are also Monal and ChatSecure. For MacOS there is also Monal.
All friendly creatures are welcome. Be excellent to each other, live humanism, no nazis, no hate speech. Not only for nerds, but the domain is somewhat cool. ;) No bots in general! (only with prior permission)