I’ve just updated/upgraded a Raspbian Buster SD card and noticed that it now contains Sonic-Pi 3.1
Running it on a Pi4 now. Not yet fully tested, and it will probably have some bugs that have been cured in 3.2dev, but at least you can run it on Buster now.
EDIT It does not appear to have erlang support or the two osmid binaries.
Consequently there is no midi or OSC support working in it.
You can see this from the log files and from looking at
dpkg -L sonic-pi and dpkg -L sonic-pi-server