Head to Due > Settings. At the top of the page is the version of Due you’re running.
On Due 22.3 and later
You can turn off these sync modification notifications in Due > Settings > Alerts & Badges > Show Sync Progress [Header] > In Background.
On Due 22.2 and earlier
You can turn off these sync modification notifications in Due > Settings > Sync > Show Sync Progress [Header] > In Background.