GA pilot reported while performing their run-up the aircraft left the taxiway onto the grass resulting in damage to the propeller.

Narrative

My planned flight was from ZZZ to ZZZ1. While conducting my runup at ZZZ and looking down into my lap at my checklist; I felt like I was moving (probably not); but accidentally let up on the toe brakes. This took me off the runup pad and onto the grass. While the plane is quite capable of operating on grass nothing seemed abnormal; as it was an unexpected excursion; I thought it would be prudent to taxi back to the FBO and inspect the undercarriage. At the FBO; I shut down the engine and inspected the undercarriage. It looked normal. I then returned to the runup area and conducted a normal takeoff. The flight to ZZZ1 was uneventful as was the landing. I taxied to the gas pumps and refueled. I then taxied to the hanger and as I was about to push the plane into the hanger; I noticed damage to both blades of the propellor. I was shocked as I did not think I hit anything with the propellor. I can only surmise that I hit one of the elevated taxi lights at ZZZ. I would not have conducted the flight if I knew I had propellor damage. In hindsight; while I didn't hear or feel anything abnormal during the event or afterwards; including during the flight; I should have realized that I could have hit something with the prop and inspected that too.