cross-device sync actually works with google drive, but the setup process can be a bit unintuitive right now. here's a step-by-step guide on how to configure it across your devices: https://ao3advancedmarker.com/syncGuideDrive.html
also, i'm currently working on redesigning the google drive login so you can authenticate directly without having to copy and share tokens between devices.
hope the guide helps get everything synced up, and let me know if you run into any issues.
