Does divorce take effect or is expiation obligatory for one who internally suspends divorce or swears an oath to himself without uttering it?

If you did not utter the divorce or the oath, then nothing is incumbent upon you, because inner thoughts are forgiven, and divorce and oaths do not occur by mere intention. Rather, there must be an utterance or what stands in its place. Al-Bukhari and Muslim narrated from Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Indeed, Allah has forgiven my Ummah for whatever thoughts cross their minds, as long as they do not act upon them or speak them." Qatadah said: If one divorces in his mind, it is nothing.

As for the person afflicted with waswasa (obsessive whispering), his divorce does not occur even if he utters it, if he did not intend the divorce, because it emanates from him unintentionally and without will. So, no divorce occurs from him if he does not truly and calmly intend it.

In summary: Nothing is incumbent upon you. It is advisable to treat waswasa by increasing the remembrance of Allah and good deeds, and by turning away from it.