1824x984 worked on my Raspbian 9 system with 1080p. Your mileage may vary. Build and inject your shared library by running:
When in full-screen mode, you can get stuck and unable to exit even when pressing Alt+F4! This could be one reason the maintainers removed the basic fullscreen capability in the first place. To avoid having to reboot, you should have ssh or serial console access handy to run a killall -9 minecraft-pi when needed.