Yes, Ex Astris supports cloud save. Like many other single-player titles, the game by default stores save data on your device. It is strongly recommended to use the cloud save feature so you may avoid losing game progress when uninstalling or reinstalling the game or cleaning up device storage space. Cloud saves are linked to the logged-in account and can be accessed across platforms.
Please note that as the game does not support auto upload of game saves, you will need to manually upload your game saves to the cloud. Thanks for you understanding!