It is optional, we use Stripe, Apple gets nothing. I am surprised there are people in software that don't know this.

No you are incorrect: If you want to sell an app for iOS, it needs to go through the App Store, and it needs to go through Apple's payment processor, be hosted by them etc, and Apple will take 30%.

There are 'work arounds' that involve being enrolled in the Enterprise Developer Program, but you're still at Apple's mercy. If they believe you're not sticking 'to the spirit of the program' (e.g. using it just to get around the App Store) they'll terminate.

Do you really believe Netflix is giving 30% to Apple?

You can't pay for Netflix from their iOS app.

I can sell an app on Apple's appstore without Apple getting a 30% cut if I use stripe?

Do you have a source for that that you can link me to? Because from this, I get the impression that is not the case: https://support.stripe.com/questions/apple-and-stripe-tos-an...

I can confirm this, it is true.

Basically, your app is not allowed to have any links to sign up, or to your website, and you can do this for eg a SaaS app.

The idea is that then you're not using the app store for marketing, it's only for servicing your existing users.