Good morning Roger, and welcome, you’ve come to he right place for information and help. I am no expert, but as a laymen, I can say that with cadence, You engage PAS (pedal assist) And all you have to do is pedal, there is no need to exert lots of pressure when pedaling. With torque, when you engage PAS, the more pressure you exert, the faster you go. Torque is more like riding a non powered bike, with power assist.
If you’re having knee problems, then personally, I would say to go with Cadence. There are lots of people on this forum that are far more qualified than me to offer advice. I thought that I would give you a general idea. Good luck in your search. BTW, I own an
Aventon Pace 500, which is an excellent bike from a wonderful company. I am extremely happy, but had the Level been out when I purchased, Level would have been my choice. Front suspension, front and rear fenders and a rear rack. Also a longer battery life. A very nice looking bike and price wise, it’s hard to beat. Aventon has cadence assist.