It definitely is not. The defining feature of a government is the legitimate use of violence. No actual or threatened violence, no government.
There are lots of reasons to be concerned about the App Store and Apple, but let's not blur the lines between money voluntarily given to use a service, and money given to avoid arrest and jail.
Violence being monopolised by State is the modern political philosophy given by Weber in 1919. Tax existed when individuals namely aristocracy even had legitimate use of violence.
Apple makes case it charges fees for public good by curating list and providing security to end users, that's public welfare unless it's millions of users aren't enough to be categorised as Public.
This App Store ecosystem sits at over 1.5 billion inhabitants, larger than China.
Frankly, state tax is the perfect word to use.
You can't not opt out of your government ecosystem (Or at least, it's more complicated).
This is like calling Walmart profit margin "tax" ... just buy in another store.
The issue isn’t the end users, it’s the app owners. A single entity controls access to the large majority of paying customers (after all, Apple makes most of the profit compared to Google/Android),
Of course you can. If you can move from Apple to Android you can move from one country to another. It would hard to find a more perfect analogy to this situation.
Why not call it a fine? Or a bonus?
Apple pretty much is the government when it comes to the App Store. A single entity, monopoly powers, no competition, makes all the rules and is allowed to enforce them without penalty. “Tax” is a pretty apt term for the 30%.