Apple watch black screen

Try restarting it: Restart your Apple Watch - Apple Support

Does the Apple logo show up?

If not, I suggest speaking to Apple Support. They will be able to offer you your next potential steps.

In my opinion, if the Apple logo isn't displaying after attempting to restart your watch, it could be a display issue. It's best to speak to Apple Support about this, though.

-- Jay (they/them)

Check to see if you have theatre mode,do not disturb or screen curtain turned on.