Pls check my other comment, anything you add to your code adds complexity and a natural lock-in. Maintainable code is not about adding every lib which crosses your way.
I see Next.js more as a build system than a framework / library. Of course it adds complexity, but in a comment above you say that "CRA does that too". You're not introducing any more or less complexity than CRA.
And what I'm saying is that Next.js does add the same complexity that you would add yourself but with great documentation. Also I have to say that's a very generic argument for any library.
Then why don't you just use the automatic code splitting of CRA?? And it's not generic, if you ever worked on a years old code base you are happy if complexity is low. Do you know if all the page transition libs will play well with Next? They do not play well even with react-router, the standard React routing lib. Code can be more complex than you might think.
SSR. CRA and Next.js are "templates" more than libraries with different aims. If you have specific arguments against SSR, just tell them because otherwise the discussion doesn't make sense.
CRA is a SPA. Next.js is not. When you hit a page in Next.js, it can prefetch and hydrate the data before it sends it down to the client. CRA cannot do this. First the client has to load the app, then the app has to fetch data from the server.