At the moment, we don’t support material, animation, or skeleton loading. This will come with a later update.
However, @texone made a nuget that loads models with assets, you can try that: VL.Assimp - wip - Forum
I am not sure whether it supports material loading.
And you can import your model in Game Studio, edit everything with the editor and load it into gamma with the Asset nodes: Create assets | Stride