Consider whether your app will actually benefit from being an SPA. Does it negatively impact the user experience to have page refreshes? Or does it provide significant benefits to do things client side? If the answer is 'no', you might as well take what is currently still easier and more standardized, and go for server-side.
But the next step is to ask these questions about parts of your app. In those cases using React or Vue or something similar for just those parts might be a good idea. And if you've already separated front- and back-end, it shouldn't be too difficult to realize (and it's a good reason to use React server-side even if that's all you use it for initially!).
So my typical applications have a handful of traditional routes serving HTML and a few small single page apps. To the extent that functionality is shared, I'll create a Clojurescript or Javascript library and reuse it. It keeps JS files small and quick to serve. I've found it to be a good balance between server-side rendering and having a massive SPA.