The VEX Forum is already supported as a mobile progressive web app. And it supports delivering notifications through the browser. There would be literally no point in any further investment in making dedicated “apps” with the current feature set of Discourse.
If you want a desktop “app,” just use a browser that supports notifications and bookmark the site (and/or make a shortcut to open the forum from outside your browser).
I am not sure why Discourse does not support PWA on the desktop. Desktop PWAs have different requirements than mobile PWAs though, so I guess they just didn’t bother.
If you want a mobile “app,” just use a browser that supports progressive web apps and notifications on your mobile platform.
Other web apps need a dedicated “app” for some of their features to work properly. For example, Discord only supports system-wide push-to-talk if you install the desktop “app” because browser security standards prevent web sites from reading keystrokes when they are not in focus. The Discord “app” is actually nothing but a website running in a typical web browser with some relaxed security (specifically, it uses the embedded variant of Chromium, which is simply the open-source version of Chrome).