Thank you for your interest in this Beta feature! After reading the document and reaching out internally, I can confirm that a registration process is required in order to be enrolled in the Beta program for Cross App Access.
It appears that this begins with reaching out to Auth0 Support or your TAM who can further assist with the enrolment process and have access to provide the form that needs to be submitted.
I cannot confirm if the process will be changed in the future for this Beta program, but at this moment this would be the official path that needs to be taken in order to gain access.