Is it permissible to work with AdSense, a company that places advertisements, 35% of which are unlawful, alongside lawful video clips that I upload to YouTube, knowing that I do not directly engage in the unlawful content and that the company takes 45% of the advertising profits?

The phrasing of the question affects the answer. The questioner is not excused by the mufti's fatwa if he knows that the reality of the matter is contrary to the fatwa. It is permissible to deal with mixed wealth, especially if the lawful predominates, such as someone who works a permissible job for a company whose capital is mixed, lawful and unlawful; in this case, it is permissible for him to take a salary. However, working with AdSense is different, as some of the advertisements you place on your videos are forbidden, and you cannot control them. What you take in exchange for displaying these forbidden advertisements is not permissible, and the fact that others publish them does not make it permissible for you to publish them.