How do you solve aeronautical and maritime applications?

The Toyota Mirai neither flies nor floats.

There's a bit of a movement for battery electric ships, but currently limited to short haul ferries. I have a suspicion this simply won't be "solved" for quite some time after car and heating electrification.

Certainly not with hydrogen directly. It might be involved in the production chain, but it's such a pain. If it's at all possible to electrify, that'll very likely win.

For flights, a combination of batteries for smaller, regional planes starting with "islands hoppers" now and SAF from either Biofuel or produced from Electricity (with Hydrogen as an intermediate step). Although I think that we might first see moves to reduce the 2x non CO2 Climate Impacts which can be much cheaper to tackle (such as Contrails).

For maritime applications, batteries when regularly near ports, probably hybrids with methanol for cross-ocean passage far away from coasts.

Hydrogen is not great for airplanes since the extremely low density makes the tanks too large. The best solution would be synthetic hydrocarbons (synthesized using hydrogen) which can outperform fossil jet fuel.