DIAGNOSIS The USB-C port is delivering power but not video data. This is a handshake issue, very common with this monitor's USB-C implementation, especially with macOS.
FIX Power cycle everything in a specific order. Turn off the monitor, disconnect the USB-C cable from both ends, shut down your Mac. Now, turn on the monitor first, let it boot to its 'no signal' screen, then start your Mac, and finally reconnect the USB-C cable. This forces a fresh handshake. If that fails, try a different, high-quality USB-C cable certified for video.
IF THAT DIDN'T WORK Go into the monitor's OSD menu (using the joystick control). Navigate to General -> USB-C Power and try toggling the setting. Sometimes switching it off and on again can reset the video data path.
HEADS UP The USB-C port on this monitor only supports up to 60W PD, not the full 96W some MacBook Pros want. If your laptop is trying to draw more, it can destabilize the connection. Use the laptop's original charger if you need full power.