So, three days later the workaround works around again, at least for these last three days.
(press start button with cover being open, 5 sec after begin of startup close cover, keep closed while booting, some secs after sim-unlock-prompt the closed cover is recognized, from then on it works until to the next boot )
As this topic is marked as "Solved" but the problem persists, I've created a new topic :
I have the same issue on my Note 9.
I cleaned the cover with some wipes for reading glasses/phone/screen/lens wipes. Cleaned around the edges, and it worked.
Something like this:
Hope it works for more people :)