Just to cap this off, as part of getting Sonic Pi working on the Raspberry Pi with the Dec 2020 update that uses pulseaudio Raspberry Pi, Pulse Audio Workaround with USB soundcard I got PureData working on it too. Previously neither the sound nor the MIDI input were working. I even found a decent synth patch that actually works.
For the sound, see the USB card workaround. For the MIDI it’s the aconnectgui utility.
In PureData, set it to use Jack for the Audio and ALSA for the Midi.
In aconnectgui (ALSA Sequencer) hit the ‘connector’ icon, and drag from Midi Through Port-0 to Pure Data Midi-in 1.
