Microsoft has addressed a known issue causing the new Microsoft Edge web browser not to install from custom Windows 10 installation media. Edge Legacy is also being removed if using Windows 10 install media bundling the KB5000850 non-security release preview update for Windows 10 1909 and Windows Server 1909. Microsoft officially released the new Edge browser in January 2020 with an installer designed to automatically replaces the browser’s legacy version. Microsoft also fixed an issue triggered by managed Windows 10 systems being updated from outdated installation media and causing Windows 10 certificates to disappear.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-iso-installs-may-fail-to-replace-microsoft-edge-legacy/