Is it permissible to inform a husband that his wife is wearing clothes that do not conform to Islamic teachings in his absence, knowing that she does not respond to advice?

You must forbid evil, and it is not permissible to let a woman do as she pleases. Continue to advise her, and if she does not respond, threaten her with informing her husband. If she does not stop except by informing him, then inform him so that he may prevent her, and remind him of his responsibility before Allah, for Allah Almighty says: "O you who have believed, protect yourselves and your families from a Fire," and the Prophet, peace and blessings be upon him, said: "All of you are guardians and responsible for your charges."