Mousey do isn't suave that head of state models (11)
I believe the answer is:
unassertive
'mousey' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?
'do isn't suave that head of state models' is the wordplay.
I cannot really see how this works, but
'state' could be 'assert' (I've seen this before) and 'assert' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for unassertive that I've seen before include "Resigned" , "Retiring" .)