Similar to the recent question about artists where you can successfully separate them from their art. Are there any artists who did something so horrible, so despicable, that it has instantly invalidated all art that they have had any part in?
I wouldn’t say the horribleness of a person is ever something that makes someone inseparable from their art. The art and the person just don’t necessitate each other. That said, I’m pretty sure someone might make a case for Nero, he burnt people on living candles and called it “art” and would lock people in concerts to hear him perform (if we assume the historical records are true). Relatedly, Saddam Hussein wrote a lot of fanfiction about defeating America with negative undertones that would make a Wattpad writer cringe.
if we assume the historical records are true
This is actually a pretty big assumption for some of the more outlandish claims. When you dig in a bit, you find many of them are kind of repetitive tropes and generally come from Senatorial-class writers about emperors whose policies were less friendly to that class.
Not to say they couldn’t have happened, and even in those days better to exaggerate than to invent from whole cloth, but it seems like an unusually large number of “bad” emperors had the same kinks as each other or the same traits that the literature had always considered “unmanly.”
