I was led to understand that the Web Push API is available in the Safari 16 Preview.
I have Web Push notifications working fine in Chrome and Firefox, using the methods described in the video at https://developer.apple.com/videos/play/wwdc2022/10098/
However, when it comes to asking the user for permission and creating a subscription using the Safari 16 Technology Preview, this fails as ServiceWorkerRegistration.pushManager
is undefined.