I found out googling around that while the option to manually allow apps from anywhere to be opened directly was removed : https://www.techjunkie.com/gatekeeper-macos-sierra/
you could still use a terminal command to make the same thing happen :
sudo spctl --master-disable
yet I ran it, then rebooted and tried running the app again, and I still got the same message preventing me from opening the app and forcing me to open it from the "Security&Privacy" menu in settings.
In a context of multiple back to back tests of my app on a fresh reinstall of mac & also new accounts, I cannot put up with it anymore I'd like to be able to do something to the mac when I use one of it's accounts for the first time (or better yet something GLOBAL that applies to ALL accounts) and not have to think about it anymore.
as per demand :
command$ csrutil status System Integrity Protection status: enabled. command$ sw_vers ProductName: Mac OS X ProductVersion: 10.14.5 BuildVersion: 18F132