It used to be possible to run Chrome apps in macOS. Then Google removed the Chrome Web Store, but it was still possible to load an unpacked app with "load unpacked" which was very helpful for development.
Now the "load unpacked" button is still there and the app can be loaded, but it seems it's not possible to run it anymore as the button to actually launch the app is gone.
Is there any other way to test a Chrome OS app than manually copying the files around for every little change?
You have a few options.
Open a tab to chrome://apps
and click on the icon for your app.
Use an app with chrome.management
permission such as AppJump to help you launch the app
Install android studio and the ChromeOS emulator and launch your app there.