That could be a solution however it's a horrible one as nearly every app on my phone is free.
I'm not about to spend 0.99 to install Facebook, Whatsapp, banking apps, web browsers, home automation apps, social network apps etc.
The solution I suggested makes the most sense - you can't host a free app on their store where the only way to unlock the content is via a 3rd party payment link.
You can have a free app but in app purchases go through Apple or you can have a paid app but subscriptions, in app purchase, upgrades etc can all be purchased with a third party link cutting Apple out.
Even if there were multiple app stores worldwide they shouldn't allow you to do that. Remove the hardware from the equation. Steam, a hardware agnostic platform wouldn't let you sell a free app in their store and then have people unlock the game for free with a third party payment link - you pay your commission to be part of a store that users enjoy managing their library in, having payments all in one place, having it sync across devices, being able to discover your content, being hosted on their servers and taking advantage of their technology like shader sharing and updated universal libraries etc.