So when it has shown where Naruto and Hinata are being held it shows them floating suspended in midair completely still. With Naruto's proficiency with sage mode as well as previously being sealed by Ishiki's sealing tech, Naruto is nothing if not a incredibly fast learner and adaptive. Writers could make it so that the last time inside Ishiki's seal he was able to understand and adapt and although he may not be able to escape he may be able to be conscious. While in suspended animation yet conscious he is able to activate Sage mode and the whole time he is suspended he is absorbing sage energy from the otsustsuki dimension. Literally years in sage mode building up massive amounts of chakra!
