Can I use vitamin C, niacinamide, and retinol together?

These ingredient names do not automatically mean the products are incompatible. The practical issue is cumulative irritation and complexity, not a blanket rule that these ingredient names can never appear in the same routine.

The ingredients are not automatically incompatible

The more useful question is whether the actual formulas and total routine are comfortable together.

Total routine load matters more than collecting actives

If several actives are started at once and irritation appears, it becomes difficult to know what caused it. I prefer one meaningful change at a time.