Is it possible to charge just once to access all the content?

I would like to limit user registration, only those who have paid for their Membership can access the content, those who have a Membership can access all the courses on the platform. Therefore the website would work by Membership and not by individual payment per course.

Is it possible to do something like this with Open Edx?

It is possible, but it will require some custom configuration/development work.

What we (at edunext) have done in the past for this use case is:
-integrate an e-commerce workflow in which the purchase of the Membership triggers a special tagging process to the user
-configure the courses with a post-enrolment filter that will control for the user tag and allow the enrollment to happen only if the user has the tag (gas a membership).
I hope this helps