Protein is the macronutrient your body uses to build and repair muscle tissue. One gram provides about 4 kcal. For lifters, protein is the macro that matters most for muscle, both when building and when dieting.
How much when building
In the meta-analysis by Morton et al. (2018), protein intakes above about 1.6 g per kg of body weight per day brought no further measurable benefit for muscle gain on average. The upper end of the confidence interval was around 2.2 g. That gives the usual range of 1.6 to 2.2 g per kg. The International Society of Sports Nutrition position stand lists 1.4 to 2.0 g per kg for most people who train.
Example: At 80 kg body weight, that range means 128 to 176 g of protein per day. These numbers are a worked example.
How much in a cut
In a calorie deficit, the risk of losing muscle along with fat goes up, especially for lean people. Helms et al. (2014) recommend 2.3 to 3.1 g per kg of lean mass for lean lifters in a deficit. Note the reference: lean mass, not total body weight. Protein-rich meals also keep you full, which makes the deficit easier.
More is not always better
According to the research, going above the upper limit brings no additional muscle gain. It does cost calories you would otherwise have for carbs and fat. Plant protein counts toward your daily total too; varied sources even out differences in amino acids. For healthy people there is no solid evidence of harm within these ranges. If you have kidney disease, check your protein intake with a doctor first.