Odd Wiring in garage - split 240 breaker into two 120 circuits
Going to a standard (15 or 20A) outlet, it should be a 20 amp breaker max (also, with 12 awg wire, the max breaker is 20 amp).
Using a double pole breaker with 2 hot 1 neutral and 1 ground is called a multi wire branch circuit. With 12 awg wire on a 20 amp breaker this would be code compliant and is used regularly to save on wire cost. The neutral and ground splits and goes with each hot.