Am I right in thinking that on the git-lab the master branch would be considered the nightly builds? If not, is there such a place to download the latest build?
We don't have dedicated nightly builds at the moment. If you're running Linux, and you previously installed OpenLP 2.9.x, you can just download master, and run it from source. With Windows or macOS, you'll need to set up a development environment in order to run OpenLP from source.