If I closed Windows Desktop App without “uploading” or “syncing” the data, will the work be lost?

2021-05-18 03:37:05 UTC 2021-06-07 03:39:26 UTC

No, before closing the App, it will show pop-up asking to save data to
local drive. So manuals which have been created half-way will still be
there when you open the App again.*But once you log out, the data that you
saved in local drive will be deleted.