If you’re asking whether any web browsers render Markdown, then I think the answer is no.
Discussion
I can only find stuff that just shows it like this: https://raw.githubusercontent.com/vitorpamplona/amethyst/main/README.md
Or as HTML, like this:
https://github.com/vitorpamplona/amethyst/blob/main/README.md
I guess there's no third option, but it seems like there should be a native way to interpret markdown in a browser.
I guess it's the same for json. Everything has to be converted to HTML, first.
Desktop Firefox will parse JSON and display it in a filterable, syntax-highlighted expandable tree.
https://firefox-source-docs.mozilla.org/devtools-user/json_viewer/index.html