In-buffer preview for Emacs own Markdown mode

Does Emacs has its own **in-build** markdown mode? I can only find elpa packages for that purpose. I can I check what packages are in-build?

markdown-mode has its own live preview function.

I think I know what you mean. But IMHO this does not render HTML in a second buffer. It only opens the systems default browser.

I don't remember offhand how I did it, and I'm not at my computer to look, but my Emacs opens links by default in eww, so the live preview works fine for me. The only challenge I have is that it opens in the same window as my markdown file, so I have to switch the windows around. Then it works great, and the eww buffer updates with every save of the markdown buffer.

Changing `browse-url-browser-function` to `eww` might be what you did.