An NDA can't ever block discussing itself - I know because I had to sign an NDA in perpetuity covering who the other signatory was on a different NDA also in perpetuity. Everything subject to that inner NDA is now completely irrelevant, but the companies involved still definitely exist and are just as litigious as ever.

I later went on to design some computer processing systems and storage systems related to US Healthcare tracking which is mostly not covered by an NDA, though the work is proprietary and not shareable, and it's much more worthy of the crazy NDA I signed in my twenties. NDAs are much more about who and less about what - if you're working restocking vending machines with Suisse Credit, you'll probably need to sign an NDA... but a more modest company doing legitimately secret stuff usually doesn't care.