As Microsoft says, support for Windows 10 version 1909 will end on May 11, 2021. As we get closer to that date, the company will try to convince users to upgrade to Windows 10 May 2020 Update or October 2020 Update.

End of support notification appears in the notification area. It will show over and over again until the user refreshes. However, not everyone is able to click on the notification to download the new version. These computers probably have some kind of compatibility issues with the May 2020 Update / October 2020 Update.