I think the idea is that hydrogen would be for energy storage and transport, not an energy source in itself. In particular it would be a good way to store energy generated during times when people aren’t using much electricity, like at night. You’d use the excess power for hydrolysis and store the resulting hydrogen for use in vehicles with fuel cells. It seems like a good way to match supply with demand, ideally with nuclear as the energy source. IMO the problem would be in the mechanics of handling pressurized hydrogen but I get the impression that it’s a manageable problem.
I recall that the big hype back in the 1990s was that it would be a source of energy, not an energy storage system.
As energy storage, if we could address the problems of hydrogen flammability and storage, the idea of fuel cells is a little more reasonable.