For [Halted] Upcoming changes that impact getting and setting memberships and access levels, everything in the “Old Endpoints” column will be replaced by the “New Endpoints” in the same row. So all of the GET endpoints will be replaced by a single GET /memberships endpoint, and similarly for the mutating calls.
I think the question in this was was about portfolio nesting, and not about the memberships within a portfolio (although the term “memberships” is definitely overloaded – in the context of portfolios, I think of it as only teams or members that have access to a portfolio, not of contained portfolios).
Something for us to think about in improving ergonomics, it can definitely be a little confusing!