"managing serves and databases"

I can spin up a new Rails-based set of droplets (aka VPSes) on DigitalOcean in about 30 minutes with some shell scripts, so that's not really an issue for an early stage startup IMHO. I've used Next.js and while it's nice as a way to bootstrap a React app, I would never use it to quickly build a robust startup product as a solopreneur. I would also never use a single data store platform like Firebase over using good ol' PostgreSQL + Redis.

Majestic monolith frameworks such as Rails and related proven architecture have never let me down in 12+ years of web app development…whereas I've been bitten many times by attempting to use the latest hotness because of a mythical future where it will have been worth that effort!