Normal people don’t care about “downgrade” or “decrypt” or “intercept” they care about availability.
But of course the easiest approved “VPN” is just data roaming.
You're describing exactly the opposite of what I found to be the facts on the ground. My connection to a residential address in the United States was allowed for a couple of days at a hostel, then blocked. It was never allowed over (Chinese) mobile data.
But it was completely fine over the internet service to my apartment. The home internet service and the mobile service were provided by the same company in a bundled plan. I was always curious what they were doing.
They aren't stupid, they're not going to insta-block everything they can detect, giving away clues to people trying to evade it.
If there's civil unrest, they can of course essentially turn off the internet, but there's a distinction between "the internet can route around censorship" and "the internet can be blocked in its entirety (or near entirety)"
1. Make it illegal to distribute a browser that distrusts their CA
2. Make it illegal to run a browser that distrusts their CA
3. Block all encrypted traffic that they can't MITM and notify police that you are running illegal softwareFurthermore, doing any of the things you listed would isolate all legitimate network traffic as well as any undesirable traffic, fully shuttering all Chinese manufacturing businesses from global requests via the web. This hat would happen then? Phone calls, emails, and even physical mail would become the new norm and most of the Chinese economy would collapse under the weight of not being able to hop on a Zoom with a client that wants tooling made for its aluminum manufacturing molds.
So besides my point of the black market your hypothesis of total control misses all the other pressures that exist that make what you’re proposing infeasible on its face. Only a place like North Korea that is willing to be a pariah state is old be willing to take the economic and social costs associated with your proposal, and they’ve only been able to do that because their abominable regime was in place before the internet existed and they pre-built controls very late in the game.
Tl;dr simply because a country _could_ do something doesn’t mean it’s realistic for reasons outside of basic networking concepts.
Doesn’t require cracking crypto or any funny business around forcing people to install stuff.
I mean... They could, though, no? If they control the gateways they could drop any traffic that isn't encrypted with some root cert that allows them to decrypt in transit packets.
I'm sure that works in a Hollywood movie, in the same way you could reverse the polarity of the lasers to enable you to travel inside the computer from a household video projector, or decrypt all the world's telephone calls using a device built into your batmobile - but this isn't a Hollywood movie and so traffic isn't in fact "encrypted with a root cert".
If for any of a variety of reasons the Chinese authorities don't want your connection to exist they'll terminate the connection, exactly as I described in my earlier comment.