Imagine if they could just order from vendors like "Solaris Bus & Coach sp z o.o."...
They're even running some
https://en.wikipedia.org/wiki/Solaris_Urbino_12_hydrogen over here that I at least hope have their hydrogen premium costs paid for by the EU grant the decals claim.
Riding them I can't note a difference between what I would expect from a battery only version.
But I can't imagine it's cheaper to take the hit of hydrogen roundtripping and the cost of hydrogen infrastructure just to avoid some 400 kW DC fast chargers at some strategic extended-stay bus stops where they take their lunch break (kick the last passenger out, walk outside, plug it in, lock the door and take a walk or go back inside and read the newspaper, and at the end unplug and hang it back on the electricity-vending-machine).
Unless it's different for bus drivers than for truck drivers, there is plenty mandatory break time under German rules to allow fast charging of such style to give enough range.
And it's easy to set up by just fitting route-after-route with the charging spots and keeping a few diesel busses in reserve to handle broken chargers until there are enough chargers to maintain bus schedules even if some of them go offline.