hello I'm using nextjs from version 12 then I stopped a bit and moved to Vite but that doesn't matter right now all I see is the new app router with RSC which feels a bit confusing many ppl like it and many ppl dislike it, me personally i preferred the pages router and found the old way of fetching data more appealing and easier to work with.. anyways my question is how does external api work with nextjs? I mean if the RSC are default components now should I be using "use client" everywhere now If I want to use for example express as my server? or how does this even work? will I need to have two servers one for frontend and one for backend?