Why a fact beats a clever opener
Founders tend to write cold email the way they pitch investors: problem, solution, traction, ask. It reads well and gets ignored, because the person on the other end didn't ask for a pitch. What earns the next ten seconds of their attention is proof you looked at them in particular.
A compliment doesn't do that ("love what you're building" fits everyone). A question doesn't either ("are you struggling with X?" is a guess). A fact does. Something from their site, their newsletter, their timetable, that they can check in seconds. Once they've seen it, the second sentence (what you do) gets read as relevant instead of as an ad.
In each template below, the highlighted line is the one only you can write. Everything else is scaffolding.