Apple should not charge a user for access to their own device. A user has paid for their device in full and should own it. A software company (ProtonMail) wants to sell the user software to use on their device. There is no need for Apple to be in the middle of this transaction, especially at 30% of any money trading hands. I have no problem with Apple charging 30% to be on the AppStore, but vendors should be allowed to install software via 3rd party stores or direct B2C.