React (and other SPAs) may be fashionable, but I generally contend that--when written well or even passably, which obviously requires an asterisk lest the Scotsmen come by but I don't think is a very high bar--if nothing else it requires developers to treat a web application as a client of an API rather than tightly integrating it. It enforces a level of separation of concerns that, IME, tends to encourage loose coupling and better design.
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.
SPA apps will decouple the backend from the front end, but the front end will always be specific to a backend in the vast majority of cases. I don't see how that is so different from templates being rendered on the server.
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.
I disagree that the frontend will be specific in even a "vast" majority of cases--if only because of the obvious proliferation of mobile. And while I agree that you can often make a good-looking server-side-rendered, templated application, I will contest that you can ever make a server-side-rendered, templated application feel correctly on a mobile device.
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. ;)
Off topic this but your phrase "lest the Scotsmen come by" intrigued me. It sounds vaguely idiomatic but I don't know the reference. Any enlightenment available?
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.