In Next.js App router should the page.js be a server component?

In Next.js 13 and above (App router) should the page.js of all the routes/folders be a server component ? I mean is it the standard practice. I know that it can be a client component using use client but is it a good practice or will there be issues during build process.

I also noticed that during build the page.js is taken as server component or something like that. Would be grateful if someone could explain this to me?