I put up a landing page early on in development and shared it on Twitter a time or two. Tweeted a few screenshots while I was working on it too.
On launch day there were a small handful of folks on the email list, and I tweeted about it, which somehow got picked up and retweeted by some big YouTubers. So that, some support by friends, and some luck.
I did have probably 6k Twitter followers at that point, but most of my audience is from teaching web dev stuff - blogging, a book, and courses around React - which has near-zero overlap with the audience of video creators. The happy comments are almost all ones I received over email and then got permission to share.
