Detailed description: https://ttntm.me/blog/static-blog-comments-hugo/
https://hugo-comments.netlify.app/
The comments posted are handled by Netlify Forms and get processed there according to this flowchart: https://bpm.wiki/diagram/Static-comments-with-Netlify-94
During the build process, the comments are obtained from Netlify Forms via their API and put into a comments.json file by Gulp. In order to make this work on localhost environments, don't forget that you'll need an .env file within the project directory that stores the necessary Form ID and API Token for your own Netlify setup.
Based on: https://css-tricks.com/jamstack-comments/