Depends on what "fix" means. Can it get people there to get out into space and turn some wrenches? Absolutely. Could it haul a new full-diameter mirror? No. I

Depends on what "fix" means. Can it get people there to get out into space and turn some wrenches? Absolutely. Could it haul a new full-diameter mirror? No. It's constrained by it's diameter, and the cargo capacity is the Dragon's trunk. Bigger rockets may be required, but nothing about the shuttle is strictly necessary there. The thing the "space plane" had that was entirely unique was the capability to load something large into the cargo bay and bring it back down. But in practice that capability was barely ever used. Starship might eventually offer that capability, but it won't be as gentle as a shuttle landing. There may one day again be a beautiful space plane, should that particular need become important again.