Is saying "I don't know" in response to the question "Are you a Muslim?" while angry considered an act of disbelief that expels one from the faith and invalidates all good deeds?

A servant must guard his tongue and ensure his speech is free from violating the Sharia (definition); it is not permissible to let it loose due to anger. As for the statement "I don't know," we hope it is not apostasy, especially since there is no inner tranquility with disbelief. As long as the possibility exists in this phrase, the default is the persistence of faith. The door of repentance is open to all servants before the soul reaches the throat.