I'm building an iOS app, and the client wants to enable the run on Mac feature. I enabled it and all run as expected on my Mac. How can I let them test it on their Macs? since TestFlight only runs on iOS devices.
How can I let them test it on their Macs?
TestFlight is not available for macOS apps. You can simply build a .app bundle for macOS and share it with directly with your client, and they can run it on their Mac.
A distribution service such as TestFlight is not needed for macOS apps, as unlike iOS/iPadOS, one can easily create and distribute apps for macOS.
To learn more about distributing testing build for macOS apps, you can refer to the following Apple Developer documents: