What is your evidence that Sheikh Ibn Uthaymeen, may Allah have mercy on him, meant by the word "mistake" in his statement that divorce occurred, especially since he mentioned in his explanation of Zad al-Mustaqni' that the divorce of one who is afflicted with "waswasah" (obsessive thoughts) for the purpose of getting rid of distress does not occur?

The divorce of a person afflicted with waswas (obsessive doubts) who pronounces divorce while aware and by choice is considered valid. However, if he divorces due to the overwhelming nature of the waswas on his mind, then his divorce is not valid, because he is not acting by choice. The cure for waswas is to completely turn away from it and not to engage with it.