When visiting sites hosting Flash content, Internet Explorer 11 will warn that Adobe Flash is no longer supported after December 2020. Adobe made a joint announcement with Apple, Facebook, Google, Microsoft, and Mozilla that Flash was being discontinued and support for it was being removed from all browsers. In the Fall of 2020, an optional update will be made available titled Update for Removal of Adobe Flash Player that will remove Adobe Flash from Windows. This update is permanent and cannot be uninstalled.
Source: https://www.bleepingcomputer.com/news/microsoft/internet-explorer-now-warns-of-adobe-flashs-upcoming-demise/