When total weekly training volume is equated, a resistance training frequency of once per week produces statistically equivalent muscular hypertrophy compared to higher training frequencies.

Study: The Resistance Training Dose-Response: Meta-Regressions Exploring the Effects of Weekly Volume and Frequency on Muscle Hypertrophy and Strength Gain

If you lift the same total amount of weights each week, whether you do it all in one day or spread it out over several days, your muscles grow about the same — this study found no big difference.

Study: How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency

If you perform the same total amount of exercise each week, your muscles will grow at the same rate regardless of whether you split that work into one session or spread it across multiple days.

Study: Resistance training frequency and skeletal muscle hypertrophy: A review of available evidence.

If you do the same total amount of exercise each week, working out a muscle once a week builds the same amount of muscle as working it out more often. The number of weekly sessions does not matter as long as you hit your total weekly target.