Hi, @thibault. You may notice that the --branch option is deprecated and replaced with --alias in the netlify-cli help info (for netlify help deploy). I’ve highlighted the two lines below:
-b, --branch=branch Serves the same functionality as --alias. Deprecated and will be removed in future versions
--alias=alias Specifies the alias for deployment. Useful for creating predictable deployment URL's
Why was it changed? Because the resulting deploys are not branch deploys.
Long story short, using the --alias option will allow you to get a predictable deploy URL but that deploy is not a branch deploy and cannot be used in conjunction with the branch subdomain feature.
If there are other questions, please let us know.