Thanks for the suggestion but that property doesn’t really help because it doesn’t tell whether the toggle should be displayed or not.
The node group input has these inputs:
The modifier shows the Input Attribute Toggle button for Color1. Translation, on the other hand, doesn’t have that toggle in this case. But a vector input could also accept an attribute in another case if it’s a field input.
An image input can never be an attribute, so that’s not a problem.
These are the attributes the modifier has:
print([k for k in md.keys()])
['Input_2', 'Input_2_use_attribute', 'Input_2_attribute_name', 'Input_3', 'Input_4', 'Input_4_use_attribute', 'Input_4_attribute_name']
So both, Color1 and Translation have the -"_use_attribute" property, even though Translation doesn’t in this case accept an attribute at all. So I would need to find some other way to check if an input is a field input.