An electric bike is a good shout.
I had a long break from cycling due to damaged knees from racing in my younger days. I took it up again in 2019 but bought an eMTB specifically because my knees are suspect.
I rekindled my joy for cycling and was doing 30 miles per day, terrain no issue. I also did gym with specific leg exercises for my knees. After a few months, I bought a normal MTB and that seemed fine, my knees were ok-ish having been strengthened.
I then bought a road bike and longer rides caused my knees to flare up again. I went to a Physio and worked with him for a short time and also changed my pedals to Speedplay because they allow far more adjustment than SPD's. They adjust at the cleat, not the pedal. In addition, I bought some orthopaedic insoles for my shoes.
Altogether, I can do 200km+ rides now without fear of knee pain.
