That’s 576 square feet. Normally, a 12,000 or 15,000 BTU mini split would do the job.
However, the level of insulation in the garage is very important. If the garage is fully insulated, then a 15,000 BTU system might be sufficient. If the garage lacks full insulation, then you should consider an 18,000 BTU mini split system in mild climates and a 24,000 BTU mini split AC or heat pump where temperature gets extreme in summer or winter.