Question about CI versions

The latest "release" in the "master" branch is the most recent stable one. It includes the user guide already built.
The user guide for the "release" branch can be downloaded separately, on the "download" page.
The online user guide on the main website should be the same version as this.

The "develop" branch is where changes are made. The user guide in it needs to be built using sphinx.

Which to use? If you are developing apps, I would stick to the release version.
If you want to contribute to the framework, then you should fork the repository and work with the "develop: branch.