In terms of having an electric feeling and probably capturing the zeitgeist of 2021, Usman vs Masvidal 2. First live event a year after everything stopped from Corona, Weidman breaking his leg, Rose getting the high kick finish, Usman putting Masvidal to sleep and following with some "super necessary" shots. Nothing interesting in terms of "good fights" but just crazy, electric moments and finishes one after the other, on the first crowded event in a year.
In terms of good fights overall...hard to say. Volkanovski vs Ortega as a main event is probably still my title fight/main event of the year, but the rest of the card was objectively trash, with Blaydes and Frozenstruik, an out of shape Nate Diaz and Valentina taking way too long to finish Murphey.
Probably have to agree that overall Usman vs Covington 2. Don't think there was a terrible fight on that PPV and the only WMMA fight was the one with Rose and Weili, which was good/interesting. Maybe Jan vs Glover since it had Yan vs Sandhagen, but then there were also gimme fights like Chimaev-Leech and Islam-Hooker, and the event slowed to a crawl thanks to heavyweights. Blachowicz vs Adesanya also wasn't too bad fight wise IIRC.