It's definitely a workaround, but I use a Chrome extension to work around this a bit. I use "Markdown Here" to add a "turn Markdown text into rich formatted text" button to my Chrome bar:
And then I use it on plain Markdown text in a GMail compose window. The rich formatted output it produces is useful for sending richly-formatted GMail messages, but it can also be copy-pasted into a Google Doc (e.g. via https://docs.new), and it comes out really nicely, including support for headers, sub-headers, links, code blocks, and the rest. The main issue is that this is a one-way process, but so long as you keep the .md source files somewhere else, this trick lets you share a richly-formatted doc with others for final commenting/editing/etc. in the GDocs interface.
https://markdown-here.com/
And then I use it on plain Markdown text in a GMail compose window. The rich formatted output it produces is useful for sending richly-formatted GMail messages, but it can also be copy-pasted into a Google Doc (e.g. via https://docs.new), and it comes out really nicely, including support for headers, sub-headers, links, code blocks, and the rest. The main issue is that this is a one-way process, but so long as you keep the .md source files somewhere else, this trick lets you share a richly-formatted doc with others for final commenting/editing/etc. in the GDocs interface.