The features provided by the add-on are really appealing. However, the latest release of the add-on is V0.18.1 from October 2021. As of now, Cappella V6.0 does not work with this old version and the VPMS project does not seem to be actively maintained in GitHub.
There is an open issue to integrate the features from the add-on into Capella itself. Is that the reason why the add-on is not maintained and we’ll see the VPMS features in a future release of Capella?
According to the documentation, version 0.19 works with Capella V6.0 and V6.1. Up to now, I have only used it with V6.0 where it works fine. With Capella V6.1, I could at least install it and reference it as a viewpoint from a project. I have not yet used it with V6.1, though.