Does triple divorce take effect on the wife if the husband had anal intercourse with her under duress, knowing that he swore by triple divorce not to have anal intercourse with her?

The majority of scholars hold that swearing an oath of divorce effects a divorce upon breaching the oath, and that pronouncing divorce three times counts as three divorces. This is the established legal opinion (mufta bihi). However, Sheikh al-Islam Ibn Taymiyyah holds that swearing an oath of divorce, when the intention is not to effect a divorce but rather to threaten or emphasize, is treated like an oath sworn by Allah, and requires an expiation for breaking an oath (kaffarat yamin) without a divorce taking place. He also holds that pronouncing divorce three times counts as a single divorce.

In this specific matter, since the nature of the duress is not clear, it appears that you were not coerced. Therefore, according to the established legal opinion (mufta bihi), your wife has become irrevocably divorced from you (bainunah kubra). You cannot remarry her until she marries another man willingly, and he then divorces her or dies, and her waiting period (iddah) ends. You must repent to Allah for anal intercourse, as it is a grave sin. It is advisable to avoid swearing oaths of divorce and to present the matter to a Sharia court or trusted scholars.