That isn’t six paths sage mode. It’s his kurama mode
There's some ambiguity with that wording though. If that text truly translates to "Uzumaki Naruto - Chakara Mode" and not "Uzumaki Naruto - Kurama Chakara Mode" then it is still left open as to what mode that is. I say this because even though RSM never had "chakara mode" in the name, it still is in fact a chakara mode (the cloaked version of it, not the base form version that kicked Madara's truth seeking ball). It is a chakara mode in the sense that it cloaks Naruto in a cloak of chakara, just like KCM and BM do.
Let it also be known that BM/BSM have also been referred to as chakara mode (Kurama chakara mode or Kurama link mode) as well, so it is not so far fetched for the same to happen with RSM.
Personally in my opinion, we will never get any real confirmation as to what happened to that form until one of the following things happens:
1. RSM is directly mentioned in the manga/anime and Naruto explains why he can't/hasn't used it.
2. Kishimoto/Kodachi do an interview and someone actually asks what happened to RSM and the writers actually outright explain it.
In my honest opinion, it would be stupid if they actually took it away from Naruto and it would be even more stupid to do so in the way that they did.
It is one thing to give a character a temporary powerup, but I believe that when a powerup is temporary, then the writers should either make that clear from the beginning or clearly show us the moment in which the character lost the power (or at least have the character say something about it). Don't just have them not use it and never mention it without giving us a proper exit for that power.
Here are two examples of good ways to send off a temporary powerup:
1. When Kakashi got DMS, it was stated from the beginning that this was temporary. Also, after Kaguya was sealed, we actually saw the chakara/eyes leave Kakashi's body and transfer back to Obito. Good job on this.
2. DBS just recently did it well with Goku's ultra instinct. They clearly had Vegeta ask "What happened to your ultra instinct?", and Goku clearly said "I can't go into it. During the tournament, I was pushed beyond my limits and just went into it on accident".
These are two good examples of how to send off a powerup.
Now here is a bad example:
1. Freaking RSM!!!
That is my two cents on it. Have a nice day.