As a novice in Shadergraph, when making vertex animation, I encountered the problem that the Position node in the vertex shader could not be connected. When I read the document carefully, I made a problem, and I hereby record it.
At this time, you need to check whether there is a texture sample in the vertex shader. If there is a texture sample, is it the Sample Texture 2D LOD used ? If not, you cannot connect
The reason is that when you output to the vertex position, the shader is running in the vertex stage. And at that moment, the GPU can't have the informations needed to auto-compute the texture LOD, thus why you need to use this node and specify the LOD you want to use.
Shader Graph Editor, doesn't let me connect wires - Unity Forum