It basically displays the forum as an app. Much better to use imo, it’s free to download from the App Store, then in the app find the macrumours forum, log in and then you can access everything as you would normally, just easier.
Tapatalk is an app that you view many forums. Been using it for years. Use it for macrumors/imore/Volvo/Rolex forums. It’s the best honestly. And I too got this message viewing macrumors website earlier on.