... Well... I just downloaded back my built .dmg file, copied the openMSX.app file to my working folder and tried it again...
MacOS said the file is Broken ! 
What a silly thing !
applying this command on the file seems to resolve the problem for me :
xattr -cr openMSX.app
I tried this command also on the file downloaded from openmsx.org, and it solve the issue too.
Hope this will help
It is good to be able to run it without any burden without the existing security problems.
Thanks for finding a good way.
hmm, I just downloaded your DMG and it also gives me the error that the file is broken. And xattr-cr is not the solution 
The xattr command is just removing quarantine on the app, which prevents Gatekeeper from checking it. That’s fine if you only distribute the app internally, but if you intend to ship the app to a wide range of users then you can’t expect them to remove quarantine because Gatekeeper is an important security feature.
The problem you’re seeing is likely caused by one of two issues:
- The app was not notarised, or notarised incorrectly.
- The app was signed incorrectly.
Macs become complicated.
more security = less fun 
