Maybe you've been using the GD2md-html plugin. I've certainly found it useful over the years, and will likely still use it for some of my workflows. https://workspace.google.com/marketplace/app/docs_to_markdow...

There was partial markdown support (and still is) in gDocs today. AFAIK copy as MD was never supported. But this new feature is full round tripping into and out of gDocs as native markdown.