Sure, but the end was visible for Roger a long time before it happened. I don't think we're anywhere close with Novak yet.
Early in his career, like back in 06, 07, 08, the book on Novak was that he was mentally weak. Would retire from a match, petulantly. Wouldn't work on his endurance or conditioning. Tons of potential, no commitment. Today, and for the last, like, 15 years, that book has mostly been flipped around. He has supreme focus, mental and physical endurance, grinds opponents down. Even in their primes it took Federer or Nadal every bit of reserve and creativity to find the shots that Djokovic wasn't expecting, to induce him to make those increasingly-rare errors. You could beat him, but first you had to conquer yourself, your own weaknesses. Clearly, few have. And I just see very little evidence that he's slipping. Losing one 5-set match, in which Djokovic continued to show that resilience, that robotic consistency in everything except (to my eyes) his second-serve variety and his net play, after a tournament where he had conquered 6 prior opponents largely with ease, really isn't evidence that his will is breaking. Nor that his body will let him down first.
Sure, the end will come eventually, as it always does. Maybe in 5 years, maybe in 3 years, maybe longer still. But I see nothing that makes me think that he's going to fall off the table, start losing matches he shouldn't, start playing like he just can't get to those balls and return them anymore. Those expecting this to be a harbinger of doom are wrong, imo, even though I can't stand the guy and am rooting for it to happen. Today he was beaten by a player who has finally risen to his level, who has proven himself a worthy opponent and rival (perhaps the first other than the Big 4). Tomorrow he will still be as imposing a figure and as tough an out. He will still be massively favored over everyone else besides Alcaraz, and likely will continue to beclown the likes of Tsitsipas, Medvedev, Ruud, and so on. There is a long journey between "losing a 5-setter in the Wimbledon Final to the world #1" and "Father Time catching up to him".