Is it permissible for a man to wear trousers and jeans, given that there is a fatwa that permits it with conditions, and another fatwa by Sheikh Al-Albani that prohibits it as an absolute prohibition?

There is no harm in wearing wide trousers that do not reveal the 'awrah (private parts) and are not considered an imitation of disbelievers, as they are no longer exclusive to them. The correct view is that wearing trousers does not fall under the prohibited imitation because the criterion for forbidden imitation in dress is for a Muslim to wear something that is exclusive to disbelievers, such that if someone saw him, they would assume him to be a disbeliever. If the clothing is no longer exclusive to them, but rather Muslims share it with them, then it is permissible to wear it, unless it is forbidden for another reason.