Things to watch out for to see how fast they are progressing:

What type of liquid hydrogen tank they use?

Whether it is a composite, aluminum with a liner, or a a full Type V composite tank, which has the potential to put hydrogen fuelled aircraft on a level where they are overtaking kerosene. No disaster if they are not there yet, and a lower spec tank is fine for the ranges and PAX they are currently targetting, but wonderful if they do make it.

Whether they manage to use one of their new HTPEM fuel cells, or stick to low temperature on this iteration?
Similar considerations as to the fuel tanks, not a disaster if it is low temp, but fabulous if they make it, and it would make Airbus far more likely to go the fuel cell route for their larger hydrogen fuelled aircraft rather than going for turbines.

One of the hassles with fuel cells is what to do with the excess heat from them,
https://www.ati.org.uk/wp-content/uploads/2022/03/FZO-PPN-COM-0019-Thermal-Management-Roadmap-Report.pdf

' he main thermal management challenge presented by hydrogen fuel cells
is the heat rejection system for the fuel cell stacks (a result of stack operating
efficiency, aircraft power demand and having to reject heat with small
temperature differences between the fuel cell and ambient air).
For near term low temperature proton-exchange membrane (LT-PEM) fuel
cell (FC) solutions, the heat rejection temperature difference can be increased
marginally (~20˚C) with the use of a vapour compression cycle. This offers
some reduction in the size of heat rejection heat exchangers, at the expense of
increased cycle complexity, and a resulting system specific heat rejection (heat
rejection rate / thermal management total system mass) of ~ 5 kW/ kg.
If high temperature (HT) PEM fuel cells can be developed, substantial gains in
specific heat rejection performance are possible due to the significant reduction
in heat exchanger size and the transition to simpler liquid coolant cycles.
The transition from LT-PEM to HT-PEM FC systems is driven by both the fuel
cell stack performance and the balance of plant performance (for which the
heat rejection system is the biggest contributor). If 2035 HT-PEM performance
targets can be met, the overall specific power of LT-PEM and HT-PEM FC systems
becomes comparable. Further increases in fuel cell operating temperature
beyond this would enable a complete transition to HT-PEM FC systems'

You have to do something with the water produced by the fuel cell too, and in view of the hazard of contrail formation some management of the release is likely

A lot of the moans about hydrogen flight are because it is more bulky than kerosene, and so simply sticking it in existing planes reduces passenger capacity.

Those fancy horseless carriages were a darn nuisance to coach makers too, who doubtless advocated keeping the pesky things separate, and attaching them to their present carriages by means of a yoke.

As Adam Smith remarked, when people in the same trade meet, even for a coffee, they conspire together against the public interest.

In this case their 'cunning plan' is to carry right on producing ever larger numbers of obsolete from the exception jets, on the ludicrous pretence that SAF will save their bacon, when they have not even managed to come up with a cover story, however fantastical, of how it is to be produced in the requisite quantity, and even the limited cases they have presented for the US only, looking at current air travel, not the vast increase they want, unequivocally shows massive impacts on land and water use, and marginal reduction in emissions.

Stuff which might work such as algae etc have a technical readiness level of zero.

I've dug out an analysis on the balance of fuel cells and batteries in a direct drive 40PAX hybrid.

https://www.mdpi.com/2226-4310/11/3/176

' 8. Conclusions
In a fuel-cell-based direct-hybrid system, a fuel cell and a battery are connected in parallel without a DC/DC converter. The voltage levels in the system are therefore directly determined by the choice and design of the fuel cell and battery. The presented work introduces a new method to determine and optimize the size of the fuel cell and battery in a direct-hybrid for aviation, considering the varying behavior of the battery and the fuel cell due to battery SOC and pressure dependency of the fuel cell. The method was used for designing several possible hybrid configurations, which were then compared with respect to weight and energy consumption from the battery and fuel cell.
A direct-hybrid system, based on the operational data of a PEM fuel cell (type HD10, Cummins Inc., Columbus, IN, USA) and a lithium-ion battery (type SLPB120255255, 75 Ah pouch, Kokam Co., Ltd., Suwon, Republic of Korea), was designed and optimized to fit the power demand of a realistic flight mission power profile. The power profile was based on the shaft power of a 40-seater aircraft of the Do328 class, which was scaled down to 100 kW.
The direct-hybrid system was designed so that both the fuel cell and the battery provide power during high power phases like take-off and climb. During the lower power phases like cruise and descent, the battery is disconnected and the fuel cell alone supplies power in order to make the best use of the high specific energy of hydrogen and to enable a long flight range. For a non-pressurized fuel cell system, the pressure dependent performance at high altitudes must be considered. As there is no DC/DC converter in this hybridization concept, the voltages of the fuel cell and the battery must match, and voltage boundaries of other components in the powertrain like the inverter motor system must not be exceeded.'

The battery helps the power for take off, and the fuel cell manages on its own for cruise and landing.

This is about the simplest possible system, as it is unpressurised, which means that there are considerable challenges with the reduced air pressure at altitude, and fuel cells need oxygen to run.

It is plain that hydrogen powered flight any rate using fuel cells not turbines has immense challenges, which I have never sought to minimise.

Rather less, it seems to me, than living on a fried planet in the interests of flying freely around it, or still worse, one where huge resources in land and water have been poured into SAF to reduce to a very small extent the consequences of such flying.