For Early Access, I started with a LinkedIn post, reaching out to close colleagues, commenting in relevant Slack groups/channels, and introducing it to some of my better freelance clients. I'll be signing up 2 more of the freelance clients shortly, with one key feature request from each first. It's important not to get stuck in the trap of developing one-off features to get each new user, but these are features that would be broadly beneficial.
Soon, I'm planning to add a super-simple demo at the top of the landing page to increase conversions, and then I'll start promoting it more. Likely also some relevant informational content marketing on a blog.