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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
Here's the upgrade guide for CSS-in-JS library authors for more info (though it's really not necessary to read this).
Styled JSX is what we're using at work right now, since we're using Next.js and it comes with this out of the box. We're actually using both SCSS modules for static styles and Styled JSX for dynamic styles. It's been great so far.
Personally, what I'd recommend right now, even if we weren't dealing with the current React 18/streaming CSS thing, is Linaria.