I can’t answer any questions related to iPhone connectivity, as i don’t have an iPhone… but i can answer them when it comes to iPads with USB-C (in my case an iPad Pro M1).
Check this comment on another thread:
Couple weeks ago i also made a short video showing USB MIDI with the original Play and the same iPad. So while in this video i use the OG Play, i can confirm sending USB MIDI also works for the Play+
