I already filed a bug and discussion on devel@ but what I'm wondering is if anyone with a Mac can test this:
https://bugzilla.redhat.com/show_bug.cgi?id=1714062
Step 1 might actually be rather important to try to reproduce the bug because it resets Gatekeeper to defaults, where if you've previously given Gatekeeper permission to run Fedora Media Writer, it might not ask again. So I suggest testing without this step first, and then redoing it with this step. And then report your findings in the above bug.
Test day for FMW only shows one result, so I think this may be real bug that slipped through the cracks. https://fedoraproject.org/wiki/Test_Day:2019-04-30_Fedora_Media_Writer#Test_...
Thanks!