You had signed out Apple ID from Mac book air If you sign out of your Apple ID preferences on Mac - Apple Support , once again sign in with same Apple ID and password with account credentials from Mac system preferences Sign in or out of your Apple ID on Mac - Apple Support
The iCloud storage has to be upgraded from your existing storage plan Upgrade to iCloud+ - Apple Support
When space is created in iCloud the files , iCloud data will start syncing , the Mac should be connected to power and high network speed is essential Work with folders and files in iCloud Drive - Apple Support
Note : when you again sign in with Apple ID make all inbuilt features like notes , mail , photos , calendar ... including safari , keychain , desktops and documents , iCloud Drive should be turned as on .
Further check your iCloud storage plan Check your iCloud plan on iCloud.com - Apple Support , and storage Check your iCloud storage on iCloud.com - Apple Support
From Mac Check your iCloud storage on any device - Apple Support