It's a mystery to me why they did not pursue home hydrogen generators that would use excess solar energy and make compressed hydrogen fuel for the car? If such attractive use case it's not technically/safely viable, that's pretty damning indication overall for hydrogen tech. Or if it was due to fossil industry wanting to stay relevant, that's pretty damning too.
They do exist, check out for “compact electrolyser”. It’s not yet commercially viable for an on-grid home systems, while off-grid installations makes pure sense. This should change dramatically when electrolyser mass production factories are operating (there are at least several such projects across the globe).
Those do exist now. Those probably not advanced enough to be widely available just yet.
That's the gist of it, high pressure electrolysis does not require any fundamental research. Had they developed it seriously, consumer units would be on the market by now.
Unless there are some fundamental problems - but these tend to be systemic, they apply to other ways of making hydrogen.