Warning: umlaut with 'mit' misplaced (9)
I believe the answer is:
ultimatum
'warning' is the definition.
(I have seen 'Final warning' mean 'ultimatum' so perhaps 'warning' could also mean 'ultimatum')
'umlaut with mit misplaced' is the wordplay.
'with' is a charade indicator (letters next to each other).
'misplaced' indicates anagramming the letters.
'umlaut' after 'mit' is 'mitumlaut'.
'mitumlaut' with letters rearranged gives 'ULTIMATUM'.
(Other definitions for ultimatum that I've seen before include "Final offer" , "Final point" , "Final warning" , "Final (peremptory) demand" , "A final demand - or else" .)