You can install DIY Solar Power Forum on your phone's home screen. It opens full-screen like a regular app, launches with one tap, and can send you push notifications for replies and alerts. It's free, takes a few seconds, and you don't need an app store.
Open the app from your home screen, log in, then go to Account → Preferences and enable push notifications. On iPhone this requires iOS 16.4 or newer and only works from the home-screen app, not from Safari itself.
In Chrome or Edge, click the install icon at the right end of the address bar to add the forum as a desktop app.