S21 Ultra screen turned black. Mobile was working.

[bashS21ultra]

Recently my S21 ultra's screen turned black, but the phone was working. I could listen ringtone and notification but couldn't see anything. It started again on it's on after 1 day.

Has anyone else faced the same problem? 

[Miatham]

Press and hold power button + volume down until you see the splash screen ( Samsung logo), then release it. Your phone will boot up.

[bashS21ultra]

I tried this. But nothing happened, i just felt vibrations but the screen didn't turn up.