something like this will do a decent job but not perfect. I try to buy umbrellas with replaceable canopies, which I replace every two years or so, with a cleaning using this type product in the meantime. available at HD, lowes, et all

I've used Wet and Forget from Costco. It worked well on my patio and brick. I haven't tried it on fabric, but it does say it's safe for that purpose.

Why can't you wash it? Ours is large and we take it off the frame every fall, wash it in the washer, dry it until damp then let air dry, put it back on and store it in the garage until spring. Our fabric is sunbrella fabric.