Has there been a prophetic hadith in Sahih al-Bukhari regarding dyeing nails? And is anal penetration not forbidden, but rather disliked, due to the absence of a hadith prohibiting it?

There is no hadith (definition) in Sahih (definition) al-Bukhari about dyeing fingernails. Rather, what is mentioned therein, and in Sahih Muslim and other collections, is the command to dye hair to change grayness, in opposition to the Jews and Christians. As for dyeing fingernails with something that prevents water from reaching them, it is not permissible unless it is removed for purification. As for a man approaching his wife from behind, there is no harm in it, provided that penetration is not in the anus, for that is forbidden and one of the major sins; due to the Prophet, peace and blessings be upon him, saying: "Cursed is he who has sexual intercourse with a woman in her anus," and "Allah will not look at a man who has sexual intercourse with a man or a woman in her anus."