Create avatar from git push

Hello,

I would like to know how I can send an icon (avatar) to the project. (Other than through the interface)

e.g., through a push on git

The avatar is not in the project, so I don’t think there’s a way to do with git.
This is done so rarely that I’ve never looked at doing it any other way than through the web UI, but you can look at the projects API:
https://docs.gitlab.com/ee/api/projects.html
to see if that lets you do it. I think that might be your only chance.