@bh4-tech with regards to the firebase plugin, it does still require use of a third-party software (that is, Firebase), which makes it difficult for some to use.
The plugin was originally developed for two reasons:
The desktop notifications plugin was unreliable on mobile devices.
Initial work for the plugin was funded.
However, after it was discovered that there was no compatibility with iOS, the funding dried up as we could not fulfil the client requirements.
That's where this plugin stands now, there is no financial backing to continue work on it.
However, looking into the MDN documentation, there is a new API that is finally getting broad adoption (as of 2023, anyway, so even better now): the Push API
It could be that this will finally allow NodeBB to natively support push notifications that work reliably even when the browser is closed.