Disable Office "UPDATES AVAILABLE" notification

You are using the click-to-run version of Office 2016. Thus, the Office updates are not controlled by Windows Update.

When automatic updates are enabled for Office clcik-to-run version, in most cases updates are applied automatically in the background without any user input. However, updates can't be applied if an Office program is open. If an Office program is open, other attempts are made to apply the updates at a later time. If, after several days, updates haven't been applied, only then will users see a notification that an update to Office is available.

To disable the update notification, we can try the following registry key settings:

HKEY_LOCAL_MACHINE\software\microsoft\office\16.0\common\officeupdate
Value Name: hideupdatenotifications
Value Type: REG_DWORD
Value Data: 1 

You can also create the hideupdatenotifications value with group policy setting to disable it:

HKEY_LOCAL_MACHINE\software\policies\microsoft\office\16.0\common\officeupdate

I got office 2019 and I did the same as Jamie did but in my case, the value had a different name.

HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Updates Value: UpdatesBlockedTime

The above key contains this string: 13192893363011, I blanked the value as Jamie did and now it doesn't show me the updates pop up.

Note: works on Office 2016 as well