The Stride 3D editor uses scene files much like other editor-first engines, but while it's probably possible to load and work with these in a Community toolkit project, there doesn't seem to be an example of how to do that.
Please create a sample project that shows how to load and work with scene files and prefabs. Adapting one of the samples from the C# Beginner tutorial template would be ideal, as that would show objects in scene as well as prefabs