But no, you can’t use a different payment system (except in South Korea). And yes, there are big apps to whom magically rules don’t apply, including Patreon or Steam. If you include the same thing in your app, you will be banned, and pointing to examples of other apps is not allowed in any appeal. Between anticompetitive rules being applied to everyone and them being applied selectively based on backroom deals, I’d rather have the Apple approach, since at least it’s fair in that regard.
Official policy is that only payments for physical goods, physical services, utilities (water, gas) and credit card payments (paying back a bank for credit card usage) are allowed to use non-Google payment systems.
But again, rules don’t apply if you are a big fish.