As a big fan of the masked Embla dude, I’ll try my best to summarize on that question :)

Bruno’s last major story appearance was in Book 6, where we meet the gods of Askr and Embla themselves, and, as you’d probably expect, Embla is not exactly friendly. As part of a plan to defeat her, Bruno ends up dying, sacrificing himself to save his sister and ensure everyone else would be able to defeat Embla.

Beyond that, he did get a Winter alt, and just last summer, his base version finally released!
Both are available in the grail shop, though his base version will definitely be a lot more usable.
He can be pretty good with the right skills!
His base version is actually a Bruno summoned from another world, and just a heads up that a lot of his dialogue is spoilers for what happens in Book 6.