Oh, sweet summer child. Of course you can ban them. Lawmakers don’t always care about the technicality of things, because in most cases they don’t have to.

You can’t prevent VPN from existing, and short of a very tightly curated whitelist of services, you can’t prevent people from actually using them, sure. Unless you’re on the side of the state, the Law, and the enforcement. In which case, you can. A blanket ban on VPN usage is the perfect gateway to “we’ve seen traffic from your house toward a known VPN server, so, blam, arrest”. And it does not have to stop at known server.

Given the regular tries to outright ban encryption, this is the perfect venue to mass target encrypted communications. Depending on the wording, the mere presence of unobservable traffic could be enough for an arrest.

If what I’m saying here sound dystopian to you, just remember that not only most of this was actually tried (and aborted) time after time, but also that until quite recently, the general public actually using strong encryption was illegal in many places, including our western countries, experiments to make state spyware mandatory are also a recurrent thing (which might take hold with the “ID verification through your phone” apps soon).