This guide describes detailed steps to setup iCloud Drive synchronization using a sample file called "myTasks.tempodo".
Enable iCloud including iCloud Drive on your Mac and your iOS Device using the same Account (AppleId).
iOS Device: Settings -> Accounts & Passwords -> iCloud -> iCloud Drive
macOS: Settings -> iCloud -> iCloud Drive
Create a new document with Tempodo and save as "myTasks.tempodo" file within the iCloud Drive folder "Tempodo".
Open the macOS Finder app and check the file is uploaded by your Mac into iCloud Drive.
Use the Apple Files App and navigate to the "Tempodo" folder. Within the folder you should find the file "myTasks.tempodo".
Navigate to Settings tab and check that "Use iCloud Drive" is activated.
Navigate to Documents tab.
Tap "Browse" to select a document with the iOS document picker.
The document browser now shows the selected file. Your are done!