If you know and like Rails and ActiveRecord especially, then one possibility, which I intend to try on my next thing, is to build an API-only Rails app (JSON only; no HTML views) and a separate Next.js app that uses the Rails app as its backend. Although it’s two apps, it seems like it would be a really nice, clean setup to work with. You can easily deploy the Next app on something cheap and serverless like Vercel, and deploy the Rails app separately on something like EC2 or Fly.io.
I have written Next apps that just connect directly to PostgreSQL, but I always end up adding other tools in an attempt to recreate something like ActiveModel and other aspects of Rails in Next.js, and it ends up turning into a mess. I think Rails+Next would avoid this problem. It would be two apps, but each would very clearly focused and would be built following the golden path of their respective frameworks. (One thing I’m not sure about yet is how I would DRYly share endpoint schemas from Rails in order to have strong typings in the Next app based on the API endpoints. But I don’t think it should be too hard to find a nice way to do this.)
I have written Next apps that just connect directly to PostgreSQL, but I always end up adding other tools in an attempt to recreate something like ActiveModel and other aspects of Rails in Next.js, and it ends up turning into a mess. I think Rails+Next would avoid this problem. It would be two apps, but each would very clearly focused and would be built following the golden path of their respective frameworks. (One thing I’m not sure about yet is how I would DRYly share endpoint schemas from Rails in order to have strong typings in the Next app based on the API endpoints. But I don’t think it should be too hard to find a nice way to do this.)