I have the Stylo 3 Plus - I have had it since June. Today was the 1st time the screen went black. First it froze - then I looked again and I thought it shut off. I tried numerous times to hit the power button on the back, under the camera lens, it would make like a vibrate sound, and the red light would flash on the screen side on the upper left. I plugged it in. Still nothing. I tried the volume keys and power button- nothing.
I have this little tool that came with my last Samsung phone- it makes it easy to remove the back cover. I simply removed the battery for maybe 2 mins. Then put it back in. Snapped the cover on it, hit the power button and it came back on, nothing was lost.
Maybe you tried this already?