I don't think anyone would say CSR is a good practice. It's acceptable if you don't care about SEO. Try using Lighthouse for example to see the score you can get.

If you include client-side rendered content inside a server-side rendered page, you will lose the benefits of SSR for that part of the page.

If a user interaction pulls data that belongs to another page, I think it doesn't hurt SEO since the search engine can still have an SSR version of that other page.