Web Push notifications work using window.PushManger which is not supported in Safari as you can see on caniuse.com or Mdn.

On Safari, you should use the object window.safari.pushNotification , documented here: https://developer.apple.com/documentation/safariextensions/safariremotenotification.

You could create a polyfill for Safari, something like this (⚠ not tested)

window.PushManager = window.safari.pushNotification

Hope this helps,

Spyna