An object with no mesh data has a geometry nodes mod that copies data from a driver object that does have mesh data. Then it applies a solidify mod and outputs the shell to a vertex group named "shell". Then a geometry nodes modifier deletes geometry with the shell vertex group.
Short description of error
The vertex group will only be deleted if the driver object has a vertex group named "shell". It does not matter if the cube object has this vertex group or not.
Vertex groups will appear in Attribute input dropdowns after using the Join Geometry node with a mesh with no vertices. So the Join Geometry node does appear to join vertex group data from a mesh even if it has no vertices, but the Solidify mod cannot write to such vertex groups. I'm not aware of any other modifiers that write to a vertex group. If there are any I suspect they might behave similarly.