This is an error in the documentation.
The top level readme says:
A Terraform provider for managing SonarCloud user groups and their permissions.
Which, while true, is not the whole story. I came to this project looking for help managing SC projects and stopped reading once I read that line at the top of the readme. It wasn't until a coworker pointed me to the TF project page that I saw a much more descriptive headline than this - and that it was (better) describing this project - that I'd already dismissed due to the above wording.