This review found that training a muscle group more than once per week was optimal for growth. However, for various reasons, no significant difference was found between training a muscle group twice per week or three times per week. Increasing training frequency is an easy to increase overall training volume, so if you’re stuck in a plateau, try increasing your training frequency to boost growth.
Source: Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016). Effects of resistance training frequency on measures of muscle hypertrophy: a systematic review and meta-analysis. Sports Medicine, 46(11), 1689-1697.