Code blocks not converted to anything
If I add a code block (see "Insert a code block" on https://support.google.com/docs/answer/10710316) to a document and try to export it, it is missing in the output with no errors or warnings. Instead, it should be exported as a markdown code block.
Docs to Markdown doesn't currently support converting smart chips (though I'll check it out when I get some time). The link you refer to only talks about smart chips and building blocks, not code blocks.
If you create a paragraph in constant-width font, Docs to Markdown will convert it to a Markdown code block. See https://github.com/evbacher/gd2md-html/wiki#text-element-conversion-features for details.
Oh, odd. It actually does mention code blocks for me when I'm logged in, so that must be a private feature. Oops :)
I ran into this also, specifically using https://www.alexwforsythe.com/code-blocks/