There's a lot of gotchas with SSR and hydration. I got bit just today because Next.js hid all the complexity from me so I was surprised when localStorage didn't work. Just popped up an error about it being undefined -- in my browser. How could that be? Took me awhile to realize it was trying to render it server-side.
I don't mean to be dismissive, but most of us still do classic SSR (like we did in 90s/00s except maybe with Rust/Go instead of PHP) and it's still awesome and resource-friendly (both for server and client).
I assume you meant there's problems with "hydrating" client-side scripts (Next.js in this case) and templates for use server-side. Which is fine if you need it! I'd just like to point out that 99% of web pages don't need any form of client-side rendering logic (apart from the browser's HTML/CSS rendering engine) and are much more user-friendly without any scripts running at all, even if you leave aside memory/privacy concerns. And if you really need some client-side interaction for some reason, i've found HTMX to be a very refreshing approach to this question.
EDIT: To be clear, i'm not saying this for you specifically, but for someone who would read through this topic and currently believes they need client-side scripting to build "modern" websites.
There's a lot of gotchas/drawbacks with the current approaches, which is why it's an active area of development. Remix, Astro, Qwik, and Marko are all taking different approaches at mixing client and server side rendering.
