You could use Next.js + any API to create an application.
You could use Next.js + a sync engine to create an application.
You could use React Router + Vite + any API to create an application.
You could use React Router + Vite + a sync engine to create an application.
From the comment above: Next.js is the opposite of a "batteries included" framework. No abstractions for ORM, background jobs, sending emails, managing attachments, web socket communication - all very basic stuff when dealing with a production application.
So if that's the battery that you need, pretty much nothing else has it except for Next.js.
These days, I tend to want a web framework to do the hard things for me rather than the tedious/boilerplate but simple things like email-sending.
And frankly I'd like to see it since that's a really hard problem to just roll your own solution. And probably a huge waste of time if you're trying to ship a real product on top of it.