Perhaps Theater Mode is active. According to Use Control Center on Apple Watch:
Use theater mode on Apple Watch
Theater mode prevents the Apple Watch display from turning on when you raise your wrist, so it stays dark. It also turns on silent mode and makes your Walkie-Talkie status unavailable, but you still receive haptic notifications.
Press the side button to open Control Center, tap , then tap Theater Mode.
When theater mode is on, you see at the top of the screen.
To wake Apple Watch when theater mode is on, tap the display, press the Digital Crown or side button, or turn the Digital Crown.