I'm currently attempting to write a calendar app for personal use, and I wanted to go the route of a self-host PWA. Notifications are a good point. How can I create notifications as a reminder before an event? Alerts are part of the icalendar standard ("VALARM"), so these are clearly notifications that are wanted by the user. Is that even possible for a PWA?
That's not true. The browser's push service wakes the service worker on delivery, even if the PWA is fully closed. That's the entire point of Push API vs polling.
And the OS will never background the browser for battery optimization reasons? Genuine question, I'm not an expert on mobile OSs (as you already guessed).