My Bolens 20hp mower blades will not disengage fully when handle pulled to appropriate position. They slow but do not stop completely

Check the linkage on that handle, there should be an adjustment. Usually this adjustment is a nut on a threaded shaft, back of the nut allow the linkage to move further.

Maybe you need a new blad or the blades have something caught in them.

Kayla, I think the blades are probably fine but they spin because the belt is not disengaging fully.

Or, it could need new brakes look around the pulleys to see what type you have, then carry model and serial numbers with you and purchase the new brakes.