Are the miracles attributed to Abd al-Qadir al-Jilani, such as his attendance at gatherings frequented by one hundred thousand people while he was seated in the air, authentic, and what is the opinion regarding miracles in general?

The specific miracle mentioned in the question concerning Sheikh Abdul Qadir Al-Jilani is not mentioned in any reliable book, but he does have other established miracles. Al-Hafiz Ibn Hajar stated that extraordinary occurrences that align with the straight path are miracles, and Al-Izz ibn Abd al-Salam said that no one's miracles have reached the level of continuous transmission (tawatur) like those of Sheikh Abdul Qadir. Al-Dhahabi narrated this statement. Ibn Taymiyyah described Sheikh Abdul Qadir as one of the upright sheikhs who enjoin performing what is commanded, refraining from what is forbidden, and having patience and contentment with divine decree. Nevertheless, exaggeration concerning Sheikh Abdul Qadir or other righteous individuals is considered a cause for deviation.