Indeed they do. It starts off working fine, but then eventually it stops. I assume they're running some AI/ML against the traffic pattern to determine if it's a VPN. I think they're light-years beyond simple traffic blocking and shaping.

I took that class (comp 116) a few years ago! Just had some fun finding and rereading my own final paper from the archives (the one you linked to makes mine seem way less interesting). Ming is a really awesome and unique lecturer.

If I may ask, why pass the perfectly appropriate opportunity to... link it here?

basically, netflow analysis tools feeding into an automated pattern matching system. 100% crypto traffic no matter what looks different than usual usage patterns. The netflow tools need some time to gather enough flow statistics between your outside-china VPN endpoint and your domestic IP, but once that's gathered, it's pretty hard to get around.

tools like obfsproxy for openvpn can help.

Why do they not outright block encrypted connections which they fail to bruteforce?

That blocks a large percentage of the websites out there now.

It's probably easier to just block all AWS/Azure/Linode/DigitalOcean/etc... blocks.