Now for SEO I want to write a bunch of blog posts. I have a friend who is not really technically but has some knowledge. What options do I have to integrate a Blogging system/cms so that he can easily write blog posts (text and image).
My thoughts we Markdown and upload images but feels cumberson. Are there any solution I could integrate easily?
I think Next.js is overkill for a simple blog. Can you just put the blog on a different subdomain and host it on Wix or Squarespace or Wordpress (if you trust them) or similar? Much easier for your friend that way.
Otherwise, if you really want to integrate it into your existing Next.js frontend, that's what headless CMSes were made for. They provide an API for you to fetch from as a dev, along with an easy GUI for your non-tech friend to easily use to compose articles with.
Ghost is an open-source one you can self-host, and there are a bunch of others (including the one I work for). See some reviews at https://www.g2.com/categories/headless-cms?utf8=%E2%9C%93&fi... or a list at https://jamstack.org/headless-cms/ (I'm not affiliated with those sites).
You can also self-host a different frontend or full-stack (non-headless) CMS on a subdomain (or a subfolder/path if you must, with a lot more routing complexity). For flat-file blogs, probably Grav or TinaCMS could work for both you and the user (because they include an editor GUI). Or else Astro is easy to deploy as a dev, much simpler than Next, but it doesn't have a built-in editor GUI so you'd have to pair it with a headless CMS (or make your own simple one).
One thing I learned is that you should lean towards letting non-technical people choose their own tools like why we largely let developers choose their own tools.