If you’re concerned about spoilers this source says there is none:

https://www.nintendolife.com/news/2023/08/sea-of-stars-making-of-documentary-is-the-perfect-primer-ahead-of-release

“If you’re concerned about spoilers, then fear not: we’ve already watched the documentary ourselves and can confirm that it doesn’t go into any key story details. Rather, the developers talk more about the technical aspects of the game, like pacing, lighting mechanics, and day/night cycles - that sort of thing.”