People used to say that. But Novak is 32 and there is NO DROP.
Even Fed had slowed down at 32. Nadal has been considerably slower since 2018, when he got to 32. But Nadal slowed down after late 20s IMO.
Djokovic is not declining physically. I don't think anything will change after 35. Yes, his motivation might drop. But his form, endurance and speed won't.
At this point, he's the fittest player on tour and it's impossible to outlast him. That confidence in the physicality gives Novak the mental belief.
As the points get longer, he knows that he will always come out on top.