Why doesn't Naruto have/use his Six Paths power?
Naruto did not lose his Six Paths senjutsu because he can still manipulate truth seeking balls, and his eyes also exhibit that he is using it in battle (tailed beast eyes crossed with sage eyes with no eye shadow).

Sasuke awakened the Rinnegan because Kabuto used Hashirama's cells to heal him after Madara impaled Sasuke with a sword. Thus, Asura's chakra mixed with Indra's chakra, becoming Hagoromo's chakra, thus allowing Sasuke to awaken the Rinnegan.

Basically, nothing has changed, except that Naruto and Sasuke can't use the Six Paths Sealing jutsu anymore because it can only be used once per lifetime and the two already used the jutsu to seal kaguya