To what extent is it valid to act upon a weak hadith, and why did Al-Bukhari include weak hadiths in Al-Adab Al-Mufrad, and did he draw attention to them, and has the Ummah unanimously agreed on the permissibility of acting upon it except in major rulings?

Al-Bukhari, in his book "Al-Adab Al-Mufrad" (A String of Pearls), did not restrict himself to only authentic narrations. Rather, he presented the chains of transmission (isnad) so that the reader could verify them. This is not a flaw, as many imams, such as Imam Ahmad and the compilers of the Sunan (traditions), did the same, as they did not commit to including only authentic narrations.