I'll flag this as I haven't been able to resolve it. The package builds and works fine on latest Raspberry Pi OS 64bit, but has a run time error on latest Raspberry Pi 32bit OS (which is the predominant one in use at present)
The error is shown in the Sonic Pi erlang log.

The on_load function for module sp_midi returned:
{error,{load_failed,"Failed to load NIF library: '/home/pi/Downloads/sonic-pi/app/server/erlang/sonic_pi_server/priv/libsp_midi.so: undefined symbol: __atomic_fetch_xor_8'"}}

I think I've found the solution. You need to link atomic in to the target_link_libraries for the armhf platform to build properly. I have it building and working changing the line
target_link_libraries(target_link_libraries(libsp_midi oscpack)
to
target_link_libraries(libsp_midi oscpack atomic)
I think the formal solution should probably include a platform test, as I don;t think yould want this on a Mac for example.

So that it is possible to filter out some messages, like midi clock.

It works ok on Windows and Linux.

Need to send the mac_midi_reproducer to the juce team and ask for advice.