In the absence of other responses, FWIW (I am not an expert but
have heard a bit):

There is definitely some interest in disability aids, but imho not
enough.

Some UK clubs have 2-seaters with hand rudder controls. At least
one 1-armed pilot/instructor flies. At least one paraplegic
pilot/instructor flies too.

The BGA approved some modifications, pre-EASA. I don’t know
what the status of such modifications now is.

(I have a passing interest too – due to wearing a caliper and raised
boot on one leg, I cannot fly as PIC on most K21s because I cannot
get my foot into the rudder pedal hoop, and several glider types I
cannot happily fly because I have difficulty in getting full right
rudder. I can just do it in my Lak 17A FES, so am happy with that.)

I wish more clubs had disability-friendly 2-seaters, but most seem
to do little or nothing until a disabled person joins them and then
they take action. One or two have deliberately adopted a policy of
accommodating disabled pilots, and i wish more had done so.

Chris N