Does anyone know of an adapter of some kind for bike brakes ?

My hands have been getting more painful as the last few years have gone by. I’ve been checked for RA by various blood tests so it seems that I have OA in my thumb joints. I won’t be able to cycle again if I can’t get help with the brakes. It’s painful trying to change gear too but I could live with sticking to the same gear. Braking is a bit more fundamental !