Really?
Check out his wins and losses this year. It's pretty horrendous. Besides the olympics, which was anything but easy, and even his wimbledon route to final with a W/O wasn't exactly high level.
He's currently serving like my grandma, slow, tons of DF's. Movement is off. Again 'one of the worst matches i played'.
Sounds like me he's not been fresh the whole year, with one execption that probably cost him tons of mental energy. Meanwhile, the rest of the field is moving along. The losses Alaraz and Sinner have had this year only strengthen them for next year as they are very young with a good upwards curve and actively building and improving. And as quickly as thses cats came on the scene, new blood will join soon too.
ND first needs to get to his 'regular' level before talking on raising his game. He cannot rely on his aura anymore and he seems uninterested.
It's up to him ofcourse, but he's lightyears away from where he was. Does he want to continue like this crashing out of tournaments for a few more years?