Yeah its a 64 bit Intel Core I7, Im used to the terminal and tried a few tweaks :
such as disabling GateKeeper (both ways) :
sudo spctl --master-disable
and
sudo xattr -rd com.apple.quarantine "$FILEPATH"
None of these methods worked.
When doing
sudo chmod 777 "$FILEPATH"
on the app I couldn't open it, I found out that doing the very same command on the archive then unzipping it solved the problem.
To avoid this problem in the future I think you should add the process in some installation guide. Or find a way to ship a .zip with the correct permissions. But most of the time to install an app on mac devs provide a .dmg that you can make with disk utility, terminal, dropDMG, (you'll need a mac your friend or I could provide the .dmg to you or through a VM) or alternatively a .iso that can be made on windows.
I can provide some tests for mac if you need them, I got some suggestions, but I saw that you prefer to add the ones of you patrons (which I can understand). On a les mêmes fuseaux horaires, je suis aussi français.