Microsoft officials provided this information in a post about Edge kiosk mode, and I would have completely missed it without Neowin.net calling it out. Microsoft's blog post advised kiosk-mode customers to install the new Microsoft Edge and set up kiosk mode before they apply the April Windows 10 patches. Those who don't do this "will experience a disruption" in kiosk mode. They noted that some of the kiosk mode features in Edge Legacy won't be available in the new Edge, but said "most" use cases will be available as of Edge 90 and full parity should be there by Edge 91.
Update: Microsoft also has another blog post, published today, February 5, on the legacy Edge browser phase out. That post notes that if the new Edge is already installed, the April update won't reinstall the new Edge and will only remove legacy Edge. The versions of Windows 10 to which this is applicable are Windows 10 version 1803, 1809, 1903, 1909, 2004 and 20H2.
While Microsoft made the new Edge part of Windows 10 as of Windows 10 version 20H2, legacy Edge remains (but is hidden) on Windows 10 PCs. As of April Patch Tuesday, the legacy Edge browsers finally will be removed from Windows 10.