How so?
Developers can make apps for other platforms, Apple won’t receive a dime. Developers can follow the rules for free apps, Apple won’t receive a dime.
Where is the extortion? The developer broke the rules, either on purpose or accident. As a result, they had to fix their app before future updates would be allowed. This is not a secret, it’s in the agreement developers sign when they CHOOSE to make apps for iOS. No one forces them to do so.
There is no extortion here.
Apple is completely up front about the costs associated with iOS apps.
You may wish those costs were lower. That’s fine. But it’s not extortion. And since Apple isn’t even close to having a monopoly on the smartphone market, there is competition.