Not right now - whatever app you have, it requires modification to the code.
I don’t think it will be possible to use this plugin with any app that you don’t own, because push notifications depend on sharing Google authentication (or other authentication if not using Google Firebase) between the forum and the app. This is so that Google knows who is responsible for potentially sending malicious or spam notifications and can shut down their account. Also the Google authentication can potentially be used to do other things with the person’s Google account, depending on how it’s set up. So I don’t think that the Discourse Hub app creators (or any app creators) would want to share their Google authentication with everyone who has a self-installed Discourse forum, and of course they cannot add everyone’s Google authentication to the app code (nor ask end users to do it after downloading). For Google Firebase push notifications, the forum and the app must be owned by the same organisation, I don’t see a way around it.