We could mandate that any platform beyond a certain (huge) size must provide open interoperability APIs.
Less radically, we can demand that any entity that takes any public money (and of course public entities themselves) avoid communicating solely through closed platforms.
It's insane that the primary public communication channel for e.g. certain UK government institutions and the Norwegian police, was Twitter at one point!
This is the correct approach. If these American companies want to operate in our countries, and maintain their positions as our primary information channels, then they need to obey laws.
We need open APIs, transparent algorithms, and above all, accountability.