I’m not sure there are any power grids past the tens-of-megawatt range that aren’t just a 2/3/4 terminal HVDC link.

Railway DC supplies usually just have fat rectifiers and transformers from the AC mains to supply fault current/clearing and stability.

Ships are where I would expect to start seeing them arrive, or aircraft.

Almost all land-based standalone DC networks (again, not few-terminal HVDC links) are heavily battery backed and run at battery voltage - that’s not practical once you leave one property.