See this:

JavaScript MutationObserver. Observing a child element after observing a parent element triggers no events

If I subscribe to a child after i subscribed to a parent i get no child events.

If I subscribe to document, I get all kinds of events, but if a parent is deleted, then I will not get an event from the parent for a subscribed child.

I do not see how mutation observers are useful at all. Is this really the alternative than to use the deprecated MutationEvent?

https://developer.mozilla.org/en-US/docs/Web/API/MutationEvent

There we have DOMNodeRemovedFromDocument DOMNodeRemoved but with the threat of them possibly stop working any given time.

I do not see how MutationObservers are replacement though.

I would need to jump hoops to get this kind of behavior and likely pay with performance.

I am not prepared to iterate all children of a parent to detect any child nodes that might have subscribed.