Earlier quoted context omitted.
If a company like Spotify sells subscriptions both in the app and on the web, they have to charge 43% more to the in-app purchaser to get the same revenue, even though the user gets exactly the same experience. I would call that a tax (informally; I know it strictly doesn't meet the definition) and as a customer I would like to know about it.
If you don't like it then don't set up payment through Apple. Just set it on the web. Multiplatform subscriptions outside the Apple ecosystem are explicitly allowed. The reality is that users don't get to save money so they don't care.
It seems Apple prevents you from embedding the website, linking to the website, directing users to that website from the app, or giving a FAQ that includes information about how the user is expected to pay via the website. Users have to guess, or already know.
Watch the struggles LTT have gone through with the Floatplane app.