Did you know you can use a QT Py RP2040 as a USB to Serial MIDI converter? The QT Py RP2040, running CircuitPython code, receives MIDI messages over USB and then sends the messages out over serial UART. You can build small add-on boards, or friends, for TRS-A, TRS-B and DIN-5 MIDI out circuits that plug directly into the QT Py RP2040.
This concept was inspired by Sandy Macdonald on Twitter. It makes for a compact and simple solution for interfacing hardware MIDI devices with USB.
Versions for TRS-A, TRS-B and DIN-5 MIDI connections are shown in this guide. You can choose which one to build depending on your hardware MIDI device.
If you aren't sure which type of TRS connection your TRS MIDI device uses, you can search for it on minimidi.world to see if it uses TRS-A or TRS-B. TRS-A is currently the MIDI standard, but many devices out there have TRS-B sockets. The difference is that the 3V and TX serial connections are swapped on the audio jack.