Success with Raspberry Pi 5

Hi Skabadee & Docdecibel,
A little clarification is missing here (my bad).
For both rtmidi and python-midi you should use the adapted versions under my GitHub account:

• python-midi, this one has a (now stale) branch, but this is to keep the python2.7 version.
  The builtin sequencer of samplerbox will not work if you use the original.
  
• rtmidi2, don't use the master branch, but the (now a stale) python3 branch. However it's the one having the needed adaptations. For some reason I never merged this in the master branch.
  

Just copy them down in your home directory and run setup..
Above is not mentioned in the notes in the download archive archive as mentioned above ...
Hans