Why is Preview Button Disabled?

I was able to preview same app before.
Now I’m able to view the app with Launch > App Preview Portal > Open.

Why can’t click ‘Preview’ button?

That’s a result of some last-minute UI tweaks – this discrepancy will be fixed in an upcoming release. Please follow at https://tracker.appgyver.com/bug-reports/p/preview-button-in-top-right-corner-is-disabled