The End of Support Calendar shows Microsoft Operating Systems end of support dates, whether they are the end of mainstream support that updates features and cosmetic changes, or extended support, which ends security fixes and all Microsoft technical support other than old web pages.
According to Microsoft's Modern Lifecycle Policy, "Microsoft will continue to support at least one Windows 10 Semi-Annual Channel until October 14, 2025."
Editorial mode ON: Yes, it's vague. This entry will be updated once there's news, but that's unlikely before early 2024.
Office 365 will stop supporting Microsoft Edge Legacy on March 9th, 2021. Microsoft Edge Legacy was forcibly replaced by Microsoft Edge Chromium in Windows 10 in April 2021, after a long period of recommending the change as optional.
As both the Legacy and Chromium products are identified everywhere in Windows as 'Edge', they can be told apart by their logos. From left to right, here are the logos for Internet Explorer, Edge Legacy, and Edge Chromium.
Windows 10, Version 1909, released late in 2019, will reach the end of security patching on May 12th, 2021.
Office 365 will stop supporting Internet Explorer on August 17th, 2021. Microsoft Teams previously stopped support for IE in 2020.
Windows 10, version 2004, named for the release date of April 2020, but known as the May 2020 update, will reach end-of-life, on December 14, 2021, and will no longer receive security patches after that date.