Does olive oil on the hair prevent the water of Wudu from reaching it, and is it obligatory to remove it before Wudu, and is washing with water alone sufficient for its removal, or is it necessary to use soap, and is it permissible to wipe over the head if it is applied after Wudu?

The head, like other limbs subject to purification, requires the removal of anything that prevents water from reaching the hair. If the oil has a solid consistency (jirm), it is considered a barrier and must be removed. If it does not have a solid consistency, it is not a barrier. It is not necessary to use soap to remove oil with a solid consistency; the important thing is that it is removed. It is not permissible for one who has a barrier on their head preventing water from reaching the hair to wipe over it.