EU asks Elon Musk to prove X isn't breaking Europe's disinformation rules

That's not what's happening here.

In general, a lot of regulation works via requiring companies to do things to prevent a bad outcome. Primary enforcement is via either audit (ie "show us what you're doing") or reporting (ie "you must tell us what you're doing on a regular basis"). A banking regulator, say, doesn't generally wait until it has examples of money laundering at bank A _before_ it asks bank A what it's doing to prevent money laundering. This is all generally pretty quiet and unremarkable, and doesn't get much coverage. When you see a regulator actually prosecuting a company, that's _kind of the failure mode_.