Is the surplus money received as compensation for a car accident, with comprehensive insurance and the fault being 100% on the other party, and which exceeds the actual value of the spare part, forbidden? And must it be returned? And to whom should it be returned?

The money you receive from the insurance company is permissible, whether the insurance is cooperative or commercial, because the impermissibility of participating does not mean the impermissibility of taking one's right. You are not obligated to spend all the money on repairing the car; the remainder of it is yours.