When imam Bukhari mentions a muʿallaq hadith with sigha al-jazm, it indicates that its chain is established in his view, so it is definitively authentic - Abd al-Haqq al-Dihlawi

Muqaddima usul al-hadith cover - Abd al-Haqq al-Dihlawi
Muʿallaq hadith with sigha al-jazm - Abd al-Haqq al-Dihlawi (Muqaddima) part 1
Muʿallaq hadith with sigha al-jazm - Abd al-Haqq al-Dihlawi (Muqaddima) part 2