Concept of license payment for Android version

Hello, can someone explain me relation of license payment to open software?

To me, I understand that “some parts” of the software are licensed to their proprietary owners and need to be paid for. That implies to me that these parts of software are not open source, therefore are closed source and that implies that this closed source is not available.

Is this assumption correct, or are all parts of the software truly open source? What is then licensed for a fee?

Thank you, Jan

Your assumption is not correct, all parts of the software are truly open source: GitHub - cryptomator/android: Cryptomator for Android

Open source does not necessarily mean “for free” as in “free beer”, see: Gratis versus libre - Wikipedia