I would imagine the author is asking a question from a company where Google Workspace is the default tool, and would like to produce document that can be shared with others in Google Drive?
You can mount Drive to a drive or mountpoint and edit it with a local tool.
You can style the document in some other form of markup.
You can use the tools given to produce the result you want.
It strikes me as modern cargo-culting to expect cloud providers like Google to cater to niche crowds. We already know they don't care very much about the long tail. If Drive isn't supporting markdown, it's pretty obvious by now that it is not a priority for them.
And the tone of the title on here is pretty damn presumptuous. It's like new gamers complaining that some new game doesn't come with photo mode, cloud save, 100% customizable clothing, etc, all these optional things that used to be ancillary but are now somehow a requirement.