DIAGNOSIS: The monitor's HDMI port is likely set to a mode incompatible with your console's signal. This is a handshake issue.
FIX: Unplug the monitor from power for 60 seconds. Reconnect. Press the monitor's joystick to open the OSD. Go to 'GameVisual'. Set it to 'Racing Mode' or 'FPS Mode'. Then go to 'System Setup' -> 'HDMI EDID Mode' and set it to 'HDMI 2.1'. Power cycle the PS5.
IF THAT DIDN'T WORK: The PS5 may be outputting a resolution/refresh rate the monitor can't sync to. Boot the PS5 in safe mode and set the HDCP setting to HDCP 1.4 temporarily to force a basic signal.
HEADS UP: Do not use the monitor's 'Variable Refresh Rate' setting with PS5's VRR enabled simultaneously. It can cause black screens. Pick one.