As new|non session management has no dependency on JACK, it would make sense for it's UI to also not depend on it, or at least have a command line flag to skip that specific test (yes I know you argue with user experience - most users will want to have JACK running, etc.)
But, it is not unusual for me to have multiple synthpod_alsa/dummy clients running under new/non session management w/o a running JACK server.
Spinning up a 'jackd -ddummy' just for argodejo to start seems really unnessary.
I expect users to slowly migrate to argodejo from the now really ugly fltk-legacy UI, so others may run into this issue, too.
I may well be the only one, but maybe not ...
I've gotten rid of that check on all of my systems for now with:
sed -i -e 's/^checkJackOrExit/#checkJackOrExit/g' engine/start.py