In terms of the Wimbledon win, I don't think Djokovic looked old, it was a battle of titans that very slightly favored the young guy. I don't think it was indicative of a Djokovic decline or the dawn of a new era of Alcaraz dominance over him, not yet at least.
While I agree that the US Open has been Djokovic's kryptonite, his last 2 appearances was him eliminating himself and a close loss in the finals to Medvedev who was on fire on the Hard Courts at that time, it's not like he's bowing out early in the tournament to tomato cans.
Now he has tons of motivation after the Wimbledon loss and all the chatter that followed starting to doubt him so this guy who has a Michael Jordan level of competitive fire is likely to be firing on all cylinders to get back on top. I know it was just Monfils but man did he look good, like he's ready to take on this Summer hard court season head on so while I'd favor Alcaraz slightly it's only slightly IMO.