i got the dark screen when i am on call. then I came across solution about sensor. I used keypad to key in *#0*# and press the "sensor" to check if my sensor is blocked. It turn out that my sensor is blocked (the test screen was GREEN). and the root cause? my screen protector blocked my sensor even though it's supposed to be clear. Guess the sensor is too sensitive and detected it even though it's transparent. After I removed my screen protector, the issue went away!
Simply pressing the Power key on my S9+ turns the screen back on.
Even if I have that button configured to end the call, it does not end the call once the screen turns off.
I had this issue for months and couldn't fix it until I contacted Samsung and they told me it is likely my screen protector, which it was. As soon as I removed it, the problem went away.
Since when is downloading an app a solution for a phone that isn't working properly?