ikjadoon I can say I've been seeing this "100% blank & black Edge window after login" symptom consistently since Beta 78, and possibly Beta 77, although I didn't record build number for myself in either case, so I can't say exact build/revision. It could not have been later than Beta 78, though, based on the dates in this thread. I used built-in feedback reporting when I reported in late September, so Microsoft should know the specific version.
Interestingly, I've never seen the symptom as reported in 80 known issues ("Edge window UI stops responding and goes dark [but UI, like parts of tabs, context menu, "..." button is still visible]") as shown in others' screenshots of Dev 79 here, or as explained in known issues as part of the workaround.
As only the later symptoms were described in known issues, then blamed on Chromium, I feel less than confident the former symptom's fixed. It's older, it occurs under very specific circumstances, it looks different, and they've had plenty of time to fix it in 79 if it was really known.