You can configure nextjs to compile as only client-side-rendering, so that it runs like before!
Another thing: NextJS is not only SSR. It’s hybrid. The advantage here is that it decreases the visible first load time.
First load pre-rendered HTML and styling is sent to the browser. So the page is already fully visible. After that all scripts and secondary CSS will be loaded. And even after that the bindings will be done.
Where as with pure CSR, all JavaScripts need to be loaded and executed and only then stuff will become visible to the user