i haven’t personally used them, but there are apps purporting to implement a (wired) USB midi controller device on iOS, which i’d think would just work on norns.
likewise haven’t much personal experience with networked midi, but there appear to be several standards for it and i’m not sure of the general state of things for iOS <-> linux. in any case if a good liniux library is identified (e.g. aseqnet?), it could be worked into norns stack as part of the (needed, eventual) MIDI overhaul.
there is also OSC, which works fine. but as mentioned isn’t generally integrated by default into scripts - it would require a bit of work in lua to set it up the way you want.