I notice you're mentioning: "We support Next.js frontends" and "Idiomatic Next.js APIs". What is it about your product that is NextJS specific? Can someone who has no interest in using NextJS still use your product?
We also have a setup wizard, which installs Stack Auth into your project, which works only on Next.js apps with the app router. It's as simple as:
npx @stackframe/init-stack@latest> Though, we do have a well-documented REST API (https://docs.stack-auth.com/rest-api/auth), so you can access Stack from any language.