DIAGNOSIS The 6 GHz band (Wi-Fi 6E) has a default setting that automatically disables itself if no 6E clients are connected for a set period. This is a power-saving feature, not a fault.
FIX Log into the router's web interface. Navigate to Wireless > Advanced Wireless Settings. Look for the 6 GHz SSID settings. Find the option labeled 'Enable 6 GHz' or similar. Ensure the checkbox is checked. Also, uncheck any option for 'Smart Connect' for the 6 GHz band to give it independent control. Click Apply.
IF THAT DIDN'T WORK Some regions require Automatic Frequency Coordination (AFC) for 6 GHz operation. Go to Advanced > Advanced Setup > Wireless Settings. Ensure 'AFC' is enabled if available. A router reboot may be required for AFC to register and enable the band.
HEADS UP The 6 GHz band has significantly shorter range and poorer wall penetration than 5 GHz or 2.4 GHz. Your device must be relatively close to the router with minimal obstructions to connect initially.