Microsoft has released the Developer of version of the Chromium-based Microsoft Edge browser for the Windows 7, Windows 8, and Windows 8.1 operating systems. This build corresponds to Chromium 77 and allows developers a somewhat stable platform to test their applications and web sites. The current developer release brings Microsoft Edge to version 77.0.197.1 and includes numerous improvements such as better dark mode support, more favorites bar customizations, and numerous bug fixes. The Dev channel is the most stable version available and updates once a week.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-edge-dev-build-now-available-for-windows-7-8-and-81/