Is ordinary multi-peptide hair serum really effective in hair growth?

Depends on your hair but mostly 99% suits this ordinary products..

Example - The Ordinary Multi-Peptide Lash and Brow Serum

Use Case and Benefits:

The Multi-Peptide Lash and Brow Serum is a light, non-greasy formula designed to support thicker, fuller, and healthier-looking lashes and brows. With 11 active ingredients, including four peptide complexes and natural extracts, this serum nourishes and protects lashes and brows while enhancing density and appearance in as little as four weeks.

How to Use:
After cleansing and drying the application area, apply a thin layer along the lash line and eyebrows in the morning and evening.