An interesting angle
I never really thought that being happy for the Prophet ﷺ could be more than just a feeling, like actually a prescribed action. It's curious seeing Ibn Taymiyyah quoted in this way, usually his stance gets presented differently.
Is there any evidence from the Quran and Sunnah that the Prophet ﷺ commanded his companions to celebrate Mawlid?
Mawlid itself isn't really the point. The point is to show joy over the arrival of the Messenger of Allah ﷺ into this world. And that joy isn't just some permissible thing according to sharia, it's something every Muslim is actually obliged to feel.