Bitcoin will continue to be useful for everyone even if that person is disabled. maybe illiterate people will have difficulty carrying out bitcoin transactions because they are hampered by their ability to see letters and numbers but i am sure that in the future the development of bitcoin wallets will continue to increase and we will see voice-based bitcoin wallets so that anyone and in any condition everyone can do bitcoin transactions easily.
in my country there are still quite a lot of people who are illiterate, but i see that they can still carry out buying/selling transactions well, because there are still many good people who guide them. i am sure this will also happen when transactions with bitcoin are carried out by those who are illiterate.