I have exactly the same issue. I was typing on whatsapp when suddenly screen get black. Notifications were ok, voice commands too. Touchscreen ok, I could use it normally when using my TV as screen with HDMI cable or with my notebook, when connected to windows or even Dex.
I already flashed fresh stock Android R rom and my display is still dead.
Tried to tap, slap, shake (I can her some noise next to camera module when shaking). I'm draining battery now with some apps that also vibrate phone. Display is still dead.
I live in Manaus/Brazil and repair centers are not working until March 23 because of Sars-CoV2. And my knox is tripped. It would cost a lot If I have to replace display or even the phone, since they probably will say it's no longer covered by warranty.
Were tou opening and closing the camera while mirroring screen? or on blind?
It seems in your case, the display went back to normal as strange as it turned off.
Could you please share the mentioned youtube video?
Hope I have that lucky as well.
Sorry for the late reply mate. The Scenario when display got back alive was.
1. My phone was connected via HDMI to TV in Mirror mode (Not Dex Mode). I also had mouse and a keypad connected since i am using Samsung Dex pad which came with my old note 9
I have from day 1have doubts about the stock camera app on my Note 20 Ultra. The app misbehaved from ranging to camera fail, and force closes on Android 10. That why i did below next
2. I forced close camera app , cleared its data and then while watching on Tv
i placed my finger on Camera icon and repeated opened it and closed it with back key.
since the display on phone was off so i used Tv for help
BUT physically doing the action on phone with fingers not with mouse on screen via mirroring
3. while i was repeatedly opening and closing app by touching the display with finger suddenly i saw camera app asking me for location tags pop up on display and from that time onward there has been no issue and the display is working as nothing wrong happened.
I wish and hope you have resolved issue by now. Please do share your experience for others . since when i had this issue, i found very less information about it. but i saw around 15 to 20 users having such issues especially with Note 20.
what i have understood is either its some issue with Note 20 Ultras Camera Firmware
or THe Electjet 45W Charger
the culprit which i bought for my Tab S7 and was using to also charge my Note 20 Ultra. I have stopped using this charger for my phone and tab and since that day only using 25W OEM charger which came with the phone. I have now this 45w Electjet charger connected via Samsung dexpad which caps its charging speed to 15W.
Here is the link of the video. and i tried all things mentioned and then after exact 24 hours
the display came alive back when doing activities i mentioned above. and i have no link with the guy or channel who posted this video. I was just trying everything to bring life to my dead display .
PS: i had only 5 percent belief in this video . i dont know what worked
i had prepared my mind for the300$ plus panel display replacement.
i just read two recent more comments which state they got their phone working back.
Do read the comments posted as there might be some more clarity of things to try.
(Please Apply reasonable pressure on screen when trying these actions as you might break the Display)