Environments are created automatically by Garden Enterprise when it receives events from that environment. If it's missing from the UI and you need it, e.g. because you're creating a secret that's scoped to it but you haven't deployed it yet, simply run any Garden command in that environment while logged in to Garden Enterprise.
When you add a project via GitHub or GitLab, Garden Enterprise clones the repository and scans it for Garden configuration files (i.e.
garden.yml files). It will create projects for all the Garden projects it find in the repository.
Furthermore, it will update the project list on every merge to the main branch. So if a new project is added to the repository, it'll become visible in Garden Enterprise once it's merged. Similarly, it'll update the name of a given project if it has changed.
Garden Enterprise receives VCS events from GitHub or GitLab, depending on how the GitHub App or the GitLab account with the associated access token is configured. To prevent this for a given repository, simply uninstall it from the GitHub App, or in the case of GitLab, remove the user account that owns the access token from the repository.