I finally made a decent documentation site for my project.
After trying 2 themes (blowfish and lotusdocs), I decided to go with HB Cards Theme - that I was already using for a blog.
This modular theme is so flexible that your imagination will be the biggest limitation.
Documentation and blogs are easy to build with Hugo. The only thing missing is easy integration with headless e-commerce solutions like Saleor or Medusa. I would really like to see working examples of e-commerce Hugo websites.