Why can't i link the output to vertex position

[mgear]

probably this one,

Why I can't connect these nodes ?

It's because SampleTexture2D uses a sample (https://docs.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-to-sample) that cannot be used in the Vertex shader. If instead you replace that SampleTexture2D with SampleTexture2DLOD, and keep the LOD at 0, it will work. We are looking into ways to make this clearer, pardon the confusion!