Old school server side rendered apps are underrated and its perfectly possible to make something that looks and behaves as well as a SPA app for most things.
Even in the case where you do have a specific frontend, I contend that there's still value in the separation because it very strongly encourages (coupled with tools like, shameless plug, nestjs-data-sec[0]) the writing of very clear viewmodels where thought must be put into what exactly should be exposed over the wire in a way that commingling database objects and template logic doesn't allow.
I think server-side rendered pages are properly rated at this point, not underrated; there are places to use them but they're shrinking as other tooling get better. As an example, even I write React almost exclusively because I write React faster and with fewer errors than any templating language I see in common use except maybe Razor (and Razor implies buying into ASP.NET, which, no). React/TypeScript are hard to get wrong and easy to burn through quickly. And I would call a React page rendered through NextJS a "server-side rendered app"--but I get the feeling you would not. ;)
Forget everything about responsiveness or whatever (which I find way more valuable than the tradeoffs one makes)--the lack of tight coupling is the real win of React and similar. I mean, if you'd like you can pretty easily build a server-side React app with NextJS and still get a lot of these benefits while using React purely as a pretty-dang-good templating language.