With respect to the non-EA charging networks supporting native 800V, "it depends". Pretty much all of the older units only support 400V (actually up to 500V) natively, Newer units are starting to support the higher voltage. It's a moving target.

In Tesla's case, they have been installing V4 pedestals which have longer cables and are 800V capable. However the power electronics in the cabinets back behind the bushes are still the 400V V3 units. Interestingly, currently the fastest way to charge a Cybertruck, which has 800V high voltage architecture, is at an EA (or other) 350 kW charger.