Windows 7 will no longer be supported, receive free security updates, and bug fixes. Microsoft installed a program called EOSNotify in the December Windows 7 KB4530734 Monthly Rollup. Every time a Windows 7 user logged into their computer and at noon every day, a scheduled task was started that launched the program. Once the date reached January 15th, 2020, the program began to show full-screen alerts that cover your entire screen, including the desktop. This allows users to make an educated decision as to whether they want to upgrade to Windows 10.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-7-begins-to-show-full-screen-windows-10-upgrade-alerts/