Also: USB hubs are dumb things. They’re like a one-to-many mult in your Euro setup: they connect many client devices to host devices. That’s it. It won’t route messages around between things; that has to be done by your host. (MIDI over USB is exactly that: it is MIDI, a serial protocol, being transmitted over USB ports and hardwrae).
MIDI, as a spec, uses IN/OUT/THRU as ports, and sixteen channels of data across a cable. If your messages are going from a CLIENT to a HOST - eg, from 16n to Norns, to get them from Norns elsewhere (say, an Octatrack), those messages have to be ‘passed on’. That could be through ‘soft thru’ - ie, echo everything back out the OUT port that you don’t care about, very common these days; that could be through a separate OUT - ie, transmit on a different output; that could be a script that reads from 16n (which by default, transmits on channel 1), and echos to, say, channel 2, with an Octatrack set up to receive on channel two.
MIDI as a spec emphatically isn’t hub/spoke; it’s devices in chains, each set up to listen for a subset of messages. This was how it was designed, around DIN cables, long ago. (When we use USB-MIDI devices, we’re essentially puting each device on its own interface, so the sixteen channels going back/forth from 16n to Norns are totally unrelated to, say, the 16 channels going back forth to another USB-MIDI device connected).
If you think this doesn’t sound like USB, you’d be right. The host-client metaphor doesn’t quite match up to the chain-of-devices metaphor. If you think this is complex, well, I’m explaining it quite badly, but it feels like you need to spend a bit more time exploring the difference between channels and interfaces, and how messages move around; it feels like some of the key metaphors haven’t quite landed yet.