Can you actually use NextJS as a back end? It's been a few years since I last worked with it. I recall it ran a server we had to deploy, but that server only did some server side rendering of the frontend.
Sure. If you deploy on Vercel you can have it serverless. If you are careful with bundles and providers you can even use only one nextjs project for the website, docs, auth, webapp, public api and whatnot.
Can you actually use NextJS as a back end? It's been a few years since I last worked with it. I recall it ran a server we had to deploy, but that server only did some server side rendering of the frontend.