You're hitting a problem I have with Ublue as well. I wanted to experiment with immutable distros last year, but Ublue provided extremely little information on how their different flavors actually differed under the hood. I ended up having to search through their forums for like an hour to find snippets of how their different when some people asked, but it was never comprehensive.

From what I recall, Bazzite had a few kernel optimizations for gaming, and received updates at a faster frequency than Bluefin, with one of the devs saying that Bazzite would be more likely to experience regressions due to it being more bleeding edge.

Looking at Bazzite's front page now, they actually seem to be doing a better job of mentioning what's unique about it than when I last tried it. But Bluefin and Aurora are still ambiguous.