...while we find it toxic it's a chief building block for things like amino acids and the like because it polymerises so easily. And apparently there's none present around red and brown dwarfs, while it's present around 30% of Sun-like stars. I wonder what that implies about Life's chances?

Hmmm... analysis of planet discovery trends indicates 30% of Sun-like stars have a Super-Earth or Mini-Neptune at least. I wonder if there's a connection between cyanide and a planet being present? If not then 9% of planets around Sun-like stars (~22% of stars) will have a planet and hydrogen cyanide for life-making. Thus 2% of stars might have a life-viable planet?

And an oxygenated biosphere might last 10% of the Main Sequence, meaning an oxygen biosphere around 1/500 of stars - about 200 million in our Milky Way. Just a rough guess. Other cosmogonic factors no doubt will alter that estimate significantly. If an intelligent species lasts ~ 10 million years then there might be ~ 1 million at a time. But the lifespan maybe too high or low, and the odds of evolution might be very low. It's pretty easy to create a list of convincing (if you squint) "pre-requisites" for intelligence to be present and produce a low, low probability. But in reality we know so little. ETIs could exist around every star bar our own and we'd be none the wiser if none ever go in for astroengineering on a large scale.