It’s surprisingly easy to get by without being able to read. I have friend who I didn’t know couldn’t read for 30 years that I knew him. His wife helped with legal papers, and he has been very successful. I’m guessing it’s even easier to get by these days. Heck, it can be very profitable to not speak or read English, or to pretend not to, because government workers are more than happy to help you take our money.
I remember a movie that starred Johny Cash as a truck driver who couldn’t read. I wondered how he could do that, without being able to read signs, addresses, maps, etc.