It's a shame indeed at this year's Toronto 1000 Masters tournament, Nadal was unable to participate due to the recurrence of a leg injury he suffered since 2005, Apart from the Toronto tournament, Nadal also has missed the Wimbledon Championship and the Tokyo Olympics this year like you say and I think it looks like the injury suffered by Nadal will take a long time to recover considering that Nadal is now 35 years old, and I also have a little doubt that later in the US Open tournament he will be able to get maximum results because in sports the age factor will certainly greatly affect the athlete's appearance.
It's not Nadal's favourite surface as well, so we might not see a good results for him.
He is on the twilight of his career, the wear and tear is not telling his body to stop for a while and take a break. Federer did it in the last 3-4 years, really just picking up tournaments that he knows he will have a high chance to win. No one can beat father time, tennis is no exception.