Facebook has now launched its non-beta app for Windows 10 Mobile. The PC version of the same app launched earlier this year. However, the current beta version still remains available to download in the Windows Store.
The feature list for the app indicates that it works on Windows 8.1 as well. The Facebook app, unlike the old Windows Phone 8.1 version was actually created by Facebook itself, rather than Microsoft.
The old Facebook beta app for Windows 10, which launched back in June, is still available to download. It's likely that the company will continue to keep this app alive to test new features and improvements before they are added to the new non-beta Windows 10 app.
Thanks to Nicholas for the tip!