In any case, you have to feed it a vector 3. You can’t have the length of a float, which is what you currently have.
The graph off to the left is a vec3 so a vec3 goes into VectorLength. Unless the Max node somehow casts to a float and takes the max of each value of the vec3? That would be a strange implementation of Max and I assumed Max is the same as in glsl (as well as clamp). It would be nice to be able to see what exactly is going on under the hood of Length though.