I find the ACSM Position Stand is a very credible source of precisely what you want to know.
Evidence category A is backed by significant Random Control Trials (RCT) with significant participants
Evidence category B is based on limited RCT studies, or a subgroup analysis, or is a meta-analysis.
Evidence category C is Non-randomized trials or observational studies.
Source: Progression Models in Resistance Training for Healthy Adults
PROGRAM DESIGN RECOMMENDATIONS FOR INCREASING MUSCLE HYPERTROPHY
Evidence category A. It is recommended that a frequency of 2–3 days per week be used for novice training (when training the total body each workout) (34,49,116).
Evidence category B. For intermediate training, the recommendation is
similar for total-body workouts or 4 days per week when using an
upper/lower body split routine (each major muscle group trained twice
Evidence category C. For advanced training, a frequency of 4–6 days per
week is recommended. Muscle group split routines (one to three muscle
groups trained per workout) are common enabling higher volume per
34 Candow DG, Burke DG. Effect of short-term equal-volume resistance training with different workout frequency on muscle mass and strength in untrained men and women.J Strength Cond Res. 2007;21:204–7.
49 Cureton KJ, Collins MA, Hill DW, McElhannon FM. Muscle hypertrophy in men and women.Med Sci Sports Exerc. 1988; 20:338–44.
116 Hickson RC, Hidaka K, Foster C. Skeletal muscle fiber type, resistance training, and strength-related performance. Med Sci Sports Exerc. 1994;26:593–8.