You can use the QT Py RP2040 with any application that supports USB MIDI, such as a USB MIDI host or a software DAW (digital audio workstation).
Plug your selected MIDI friend breakout into the QT Py RP2040 before plugging in any cables. Then, connect the QT Py RP2040 using a USB-C cable.
If you're using the QT Py RP2040 with a DAW, you'll want to setup a MIDI track and set the CircuitPython Audio device as a MIDI output. This will send the MIDI track out to the QT Py RP2040 so that your TRS or DIN-5 MIDI device can receive the data.
If you're using a TRS MIDI device, be sure to connect your device to the MIDI friend breakout with a stereo audio cable. If you aren't sure whether your hardware uses TRS-A or TRS-B, you can search for it on minimidi.world.