Microsoft has started sending alert messages to the users who are still running old version of Windows 10 v1909 for which the support going to be stopped from May 2021. Currently Windows 10 is running in 21H1. With the alert message people can upgrade first to May 2020 update and then to October 2020 update.
Also, Microsoft has added a notification it will check and confirm whether the PC is ready for the update.
Some people have spotted a message as ““The Windows 10 May 2020 Update is on its way. Once your device is ready, you’ll see the update available on this page”.”
You can check the version of the windows 10 you are using by right clicking on “This PC” from the File explorer. It will show you whether you are running Windows 10 v1909 or higher version. Alternatively , you can update the windows via Windows Update assistant page. Do remember it is always good to have latest updates installed on the PC to safeguard against Viruses and other issues.
Source: Windows latest website