I'm not a Mac expert, but I can tell you that Catalina (10.15) comes with python 2.7.10 pre-installed. It also seems to know about python3, but this gives a warning (error):
xcode-select: error: tool 'python3' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
I'm not sure what that means.
I did the following:
tar xf /mma-devl.20.02e.tar.gz
cd mma-bin-20.02e
python mma.py -G
AFAICS
python mma.py behaves normally. A small
mma does the rest:
#!/bin/sh
exec python <location of mma>/mma.py ${1+"$@"}
I also tried mma-gb. It starts up slow (parsing the grooves takes one second per groove!) and gives a deprecation warning that the system Tk is obsolete. I couldn't get it to work, it's too slow.
Hope this helps...