Good call on posting the videos - definitely making it easier troubleshoot.
Your problem is right here - the variable type of the Spline Variable is set to “Joe Fixx.”
You’ll need to switch that to be your Spline Blueprint type. When you do, you’ll get a warning, but accept it anyway. You’ll probably get some errors in your blueprint when you try to compile - just delete any old “Spline” nodes, and drag the variable back in and hook them up the same way.
What’s happening here is the variable type tells Unreal what kind of information is in the variable. This code is looking for a Spline Blueprint Actor that has a SplineComponent. Once you switch this over to be your Spline Blueprint Class, you can pull down that dropdown in the scene and select the spline actor you want to move it on. You’re currently seeing the Joe_Fixx dragon show up in the dropdown option, because the variable is set to be the Joe_Fixx dragon variable type.