Using Nuxt.js will have no effect on Phoenix’ performance.

Nuxt.js is a way to achieve SSR using JS. You would typically reach for it if you need a single page application where render speed and search engine optimization (SEO) matters. This is not always the case (e.g. the SPA is behind a login and the user reaches a landing page first).

Using default Phoenix with its templates gives you SSR out of the box. You don’t need Next.js unless your app is heavily interactive with a lot of JS.

Thank you for providing all these answers and help me get a better idea of what I will have to do.

Really appreciate it

Do you mean https://nuxtjs.org? (if so it might be worth adding some additional info to your post )