The auto scanner of default branch and pull requests works great and the GitHub App.
But is it possible in the Web UI for a developer to scan a branch before creating an actual pull request?
Indeed the Autoscan feature is setup in a way that it only triggers new scans when a commit is pushed in your master branch or your PR. We don’t make any difference between a normal PR or draft mode, it will trigger an analysis in both cases. And from the UI there is currently no way to trigger or force an analysis of a PR.
I’d say that SonarLint is your best bet to detect issues before you even create your pull request, you should definitely give it a try!