It’s not exactly 30%. For sales below $1M, it’s 15%: developer.apple.com/…/small-business-program/

In Europe, where this was established last year, they started charging a Core Technology Fee to cover the cost of hosting and data transfer: developer.apple.com/support/core-technology-fee/

And if you switch payment providers, you have to pay at least 2.5% plus transaction and any intermediary fees.

It’s nice that Proton is offering a discount, but for everyone else there may be additional ongoing costs.