This is more than mere interop, this is Europe forcing Apple to share tech.

No, it's generally just interoperability. Europe isn't forcing Apple to transfer ownership of any of their tech or IP (that's what we're doing with TikTok) - they're forcing Apple to open up access to their systems so that third party developers of software and peripherals can interact with it.

That's a perfectly legitimate exercise of sovereignty. They get to set the rules for how people do business in their countries. Foreigners have to follow the rules, too. If they decide that they do not want a "walled garden" type of product ecosystem in consumer electronics, they're allowed to do that. And they're allowed to require foreign companies like Apple to follow those rules when they do business there. That's what sovereignty is. It's why we get to keep using the imperial system of measurements (to use a minor example), even though that imposes some stupid unnecessary costs on many foreign companies and even though we're almost the only country in the world (other than Myanmar and Liberia, and <archer>you never really think of those other two as having their shit together</archer>).

That doesn't make what they're doing a "tax." Indeed, the very size of the penalty makes that implausible. It's sized to such an amount that there can't be any expectation that Apple will simply pay it as the cost of doing business there; it's so enormous that it can only have the effect of forcing Apple to comply with the rules.