chyeah

Ah, you are correct. I missed that aspect of your question.

Prismic's "slices" might be what you're looking for if you want out-of-the-box functionality and hosting.

If you're wanting a bit more flexibility from a code-perspective (and you don't mind TypeScript), I've found Payload CMS to be a great option to build out a page builder as you've described using their "blocks".