Nation states definitely can by using port targeting, traffic heuristics, and DPI. The US historically has not done this but several other states have. Even if protocols are preserved, I wouldn't want to be in a situation where I have to run a client on my local machine that consumes from the protocol. I want to be able to use a hosted client.

A user should be able to use another person's hosted Mastodon instance or Bluesky AppView/Relay.