How to gain muscle mass?

I've been going to the gym for about five months, but now I want to take it more seriously. I've noticed some physical changes, but my weight has actually gone down. My goal is to build muscle while losing body fat at the same time. I’m also planning to schedule an appointment with a nutritionist, but I need to get some routine tests done first.

My info:

• Age: 20
• Height: 1.70m (5'7")
• Current weight: 67.1kg (148 lbs)
• Physical activity: Gym 5x a week + ~7km (4.3 mi) walking/running daily

Bioimpedance results:

• BMI: 23.7
• Body fat percentage: 18.8%
• Skeletal muscle mass: 41.4%
• Visceral fat: 5%

Smartwatch results:

• Weight: 67.1kg (148 lbs)
• Body fat percentage: 21.1%
• Skeletal muscle mass: 28.8kg

Current diet:

• Breakfast and afternoon snack: Tapioca with cheese and tucumã + whey protein shake with cocoa.
• Lunch and dinner: Some protein (e.g., chicken, fish, beef) with rice and salad.
• Dessert: Mostly fruits, especially grapes.
• I don’t track calories or macros.

Thanks in advance for any advice and sorry, I don't really know how to take pictures