LOLZ. Breakeven at 12%? You're out of your mind. Their margins on the App Store have been estimated to be close to 90% (based on the 30% cut). It's not costing them an avg. of 12% to process transactions and to provide tools and other services that are completely scalable at a very small incremental cost of scale. Apple could charge 5-7% and still make billions in profit.
The App Store is enormous, processing payment transactions is a tiny part of what it does. It's a world wide operation in >40 languages. Thousands of apps are submitted per day.
12% is a guestimate I made once based on the 2019 financials (or maybe it was 2018).
Lets see if I can do the same for more current numbers.
According to CNN, 2020 App Store revenue was $64B. Apple's take is about 28% ( 30% for the big bucks developers, 15% for the rest ).
So, Apple got about $18B from that.
Gross margin for services for Apple in 2020 was 70%.
That is higher than most years because people were spending more because of lockdowns and such.
It's a pretty normal percentage for services, Microsoft for example, being a services company gets about the same for all of their revenue.
So $18B * 30% = $5.4B is what Apple needs to run the App Store.
$5.4B is about 8.4% of $64B.
So Apple would need about that to break even.
Except that the 70% is gross margin for all of services. I'd guess that it would be lower than that for the app store because it is more work, by more expensive people, than the other parts of services.
So, 8.4% is probably too low and more is needed for the app store to break even.
Remember that about 85% of apps are free and contribute nothing.
Each paid app has to support 6 or so free apps.
Also, by Apple's reckoning, their take on the whole "App Store Economy" is just 3% or so, 30% of 10%.
Because just 10% of the "App Store Economy" goes through Apple. The rest is Netflix, Uber, meal delivery apps, etc.