Starting Aug. 1, 2020, Intuit will no longer support the Internet Explorer 11 (IE 11) browser for QuickBooks Online and/or QuickBooks Authorization screens.
IE 11 and older versions do not support the latest features other browsers provide, so as Intuit continues to increase the number of online applications available to QuickBooks customers, they want to make sure they continue to provide the latest browser features for their developers.
This allows you to have access to the latest UI experiences, and creates a better experience for their mutual customers.
Here is their recent blog article for details