Microsoft Edge Legacy has officially reached the end of life today. Starting tomorrow, the web browser will begin displaying notifications telling users to switch to the new Chromium-based Microsoft Edge. Microsoft added a new Group Policy with the March 2021 cumulative updates that you can use to turn the notifications off. On April 13th, 2021, Microsoft’s Patch Tuesday will automatically install an update that removes Microsoft Edge legacy and replaces it with the new. Microsoft Edge will no longer display the notification in the browser. It is not known how much time has to go by before a notification is shown again.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-edge-legacy-will-now-prompt-you-to-install-chromium-edge/