Here I wrote what helped me resolve the issue: https://developer.apple.com/forums/thread/725772?answerId=746678022#746678022

Hey Graagas! I am also struggling to get Push Notifications working on iOS 16.4 developer beta in Safari. I added my webpage to the Home Screen. But when I request permission, I get: ReferenceError: Can't find variable: Notification (similar code as you) The same is working fine on other major browser like Chrome. Are there any further steps needed to make Push Notifications work? Did somebody make it work? Any help is appreciated!