QT has been around for decades. So has GTK. Bindings for whatever language you could possibly want. Runs on whatever OS you want. We've had "truly portable" UI frameworks since the late 90s. This has not been an issue for my entire adult life. 20 years ago, I was using desktop applications that ran on Mac OS X, Windows, and *nix with no modifications. They were written in Python, used GTK, and just worked.

Web apps are popular because 1) people don't like installing things anymore for some reason and 2) it's easier to justify a subscription pricing model.