So, I came up with this self-hostable solution (https://github.com/AlisterBaroi/markdown-to-google-docs-mcp). An application and MCP Server that can convert your (local) markdown files into Google Docs and save them into your Google Drive. Use the webapp, or just connect with the MCP server, whichever approach you want to use, the outcome is the same. It comes built-in with Firebase authentication (OAuth 2.0) + Firestore for session management and for user's google docs formatting preset, to be saved to their profile.
Play around, start the project (to show me some love), and feel free to contribute.