This notification is called "End of Support" or "End of Life" and is shown when the user launches Internet Explorer web browser.

It automatically opens a new tab in the browser containing download page of IE11.

prevent it from being auto-installed until testing is complete.

The Microsoft document here refers me to KB 946202.

Microsoft is offering help for enterprise customers -- organizations with more than 500 employees -- looking to upgrade browsers before the cutoff.

And that might be needed in some cases: Big companies and governments can be slow to move to the latest software because making those changes can be complicated to roll out across their organizations.

However, the information in KB 946202 seems dated and vague.

Basically it tells you to disallow automatic approval of Update Rollup packages.

This notification is not displayed on every launch of Internet Explorer.

Once the notification is shown and you close the tab, it waits for 72 hours i.e.

PS: In future, if you want to enable notification to upgrade to IE11, delete the FEATURE_DISABLE_IE11_SECURITY_EOL_NOTIFICATION key.