You are likely stuck at one of these two points:
If you are playing on older hardware or backward compatibility: prince of persia the forgotten sands the observatory bug fix
: Since the game uses a single auto-save slot that may become permanently bugged, many players bypass the section by downloading a save file from just after the Observatory. Be sure to disable Cloud Saves in Ubisoft Connect (formerly Uplay) before replacing your files, or the game will overwrite them with the bugged cloud version. You are likely stuck at one of these
This is the most famous community-discovered solution. You can bypass the broken lever mechanism entirely by sequence-breaking the level geometry. try these technical fixes:
If reloading a previous save does not work, or if the game crashes when entering the room, try these technical fixes: