Possibly they could force him to divest from whatever legal entity Twitter operates under in that country, or force Twitter to stop operating in that country, but they would have no authority over the US corporation.

The post I'm replying to is arguing that fiduciary duty would force the sale, not a law. The banning just... sets a chain of events in motion.

Depends on the political power of the entity and it's existing laws.

In your example, Musk could stop the app in the EU, much like TT is/was doing.

With this said, is the EU law written like the long standing US laws that give the TT law the power it has? If they have to enact new laws that would conflict with its member states wishes/dealings with other nations, expect it go to nowhere.

It won't. It would be fantastic if the EU banned Meta or X. Instead they're suddenly scared of continuing to fine them for their endless illegal data harvesting and gatekeeping to cozy up to Trump.