UPDATE: Solved in Version 18.104.22.168 (Official build) canary (64-bit)
Version 22.214.171.124 (Official build) canary (64-bit)
in Windows 10, go to YouTube, play a video in the new Microsoft Edge Canary, then press Windows button + L, to lock the user account. there will be a small area at the bottom right corner of the lock screen showing the YouTube video being played in the background and gives you the option to pause/resume or next/previous, the usual controls. in this Edge version the pause/resume button doesn't work.
doing the same thing in Chrome 76 and now chrome 77 (both canary), works fine.