I wrote up a post in another thread about new H.265 support in Blue Iris 5.9.9.99 (a.k.a. Blue Iris 6 beta) and UI3, and I'm copying it here to increase awareness.
H.265 encoding was added in some of the earlier Blue Iris 5.9.9.99 releases (a.k.a. Blue Iris 6 beta) and I already got it working...