NWjs files can't be opened on macOS becauase they're "damaged and can't be opened"

I've never had issues with this before, but every macOS export I make now returns:

“app.app” is damaged and can’t be opened. You should move it to the Trash.

Is the export function broken?

macOS now has very specific requirements about permissions (you must extract the exported zip on macOS) and security (you must now always at least ad-hoc sign an app for it to be allowed to run). The most up-to-date advice is in our guide on the macOS WKWebView exporter, which although is for a different export option, the requirements regarding macOS running apps is the same. Construct's macOS WKWebView export option also exports some helper scripts to make this easier - if you use NW.js you'll need to do the same things manually.

macOS now has very specific requirements about permissions (you must extract the exported zip on macOS) and security (you must now always at least ad-hoc sign an app for it to be allowed to run). The most up-to-date advice is in our guide on the macOS WKWebView exporter, which although is for a different export option, the requirements regarding macOS running apps is the same. Construct's macOS WKWebView export option also exports some helper scripts to make this easier - if you use NW.js you'll need to do the same things manually.

Would not following these steps return a message about the app being broken though? Because usually when apps are non-signed, macOS will be pretty explicit about it being a security issue.

Possibly, it depends on what you did. For example extracting the files on Windows and then transferring the files to macOS is known not to work, and so that might show that message.