Objective: I am trying to test all aspects of Speckle to see if we can use it for managing large amounts of geometry and multiple projects in transport infrastructure programmes (again).
Issue: Fallen at the first hurdle - loading the Revit Plugin for Revit 2023 through the package installer.
Looking at your Revit toolbar, that is most likely due to a conflict with another installed plugin and unfortunately there is very little we can do to help in these situations.
What I can suggest is to deactivate the other plugins until you pinpoint the conflicting one. To do so you can simply rename the other plugin manifests from samplerevitplugin.addin to samplerevitplugin.addin_disabled.