Easily the Last Jedi. Though I'm thinking of "worst" in the sense of did the most damage and fell the farthest from expectations. In a way, that's the only fair way to rate what "worst" is.... I mean, how do you compare epic, almost unbelievable mishandling of valuable franchises (which most people can at least stand to sit through once) against a movie like "the Human Centipede." The former is a testament to an insane mishandling of something with tremendous cultural appeal, the latter is just some disgusting joke that no one even bothers to watch after they hear the disgusting premise.
I'd say the WarCraft movie takes second place.... kind of a distant second though. The Last Jedi being that bad and that damaging was actually a surprise, the level of incompetence it demonstrated by a mega corporation like Disney was something you wouldn't have expected after what they paid to buy the franchise. The WarCraft movie being bad was not entirely unexpected (it was, after all, another video game based movie), but you still couldn't help but hope they'd do well. They really had a lot to work with and a lot of time to plan that one out, and by the end it just feels like a misfire on everything.
I know some people will say Rise of Skywalker, but really, there was no recovering after Last Jedi. Last Jedi was kind of like a passenger in a car wanting to do a course correction, grabbing the wheel from the driver and jerking it, and sending the car plummeting off a cliff. Rise of Skywalker was like letting the driver take back the wheel mid-plummet. You can't really ruin the character of Luke Skywalker and kill him off, fail to develop the new main characters in any meaningful way (I suppose Poe learned a lesson that he shouldn't question incompetent authority), waste any chance to move the plot forward and fail to foreshadow a coherent resolution to any arc, and expect the following movie to be a satisfying wrap up to a trilogy that wasted its entire middle installment.