Hello!
The Texture Object node serves as a reference to a texture that can be sampled by several
Texture Sample nodes, allowing you to avoid the needless duplication of textures.
Using the "Normal Create" function that we provide requires that you connect a Texture Object and Texture Coordinates nodes to it in order to produce a normal texture for it, which you may further tweak via the Offset and Strength inputs.
In order to to modify or use only certain channels in this context, you'd have to either use a Texture Sample node and adapt the function to accept its RGBA as an input, which would likely require further adaptation on the function's inner workings, or manually perform the intended calculations for the effect you wish to achieve within the function itself, by editing it through double clicking its node, for example.
Please let me know if this helps, thanks!