Some materials, demos, papers or components are public.
MX² has code and documentation available on GitHub.
MAX is designed to make concrete parts of the system verifiable.
For example, on iPhone it is possible to observe that identity and keys are generated locally, even without a network connection. Also, using the public MX² code, it is possible to compare the behavior of the format and check the consistency between what is generated in the app and what is reproduced by the public code.
This is not equivalent to a complete audit of the whole ecosystem and should not be presented as external certification.
It is, however, an important technical signal: MAX does not only ask for trust, but tries to make its fundamental steps inspectable.