https://support.microsoft.com/en-au/office/resolve-the-0xe4020040-store-busy-retry-later-error-in-onenote-f79f0b54-a347-44d1-b4a9-e13441f2b6a9
Resolve the 0xE4020040 (Store Busy Retry Later) error in OneNote - Microsoft Support
Find out how to sync your notebooks so you can fix the Store Busy Retry Later error (0xE4020040) in OneNote.