Unfortunately for mac users, the itch app may be required:  https://itch.io/docs/itch/integrating/platforms/macos.html

"For players that are not using the itch.io app, you might get reports of your app being "Damaged and can't be opened" and that it should "be moved to the trash".

Player who do use the itch.io app do not encounter these issues, so you may want to encourage them to use it."