DIAGNOSIS The dedicated "Gaming Port" (the red LAN port) isn't magic. It's just a LAN port pre-configured in the firmware to be the target for the Gaming QoS rules. If QoS isn't set up or is disabled, the port does nothing special.
FIX Plug your Xbox (or PC) into the red Gaming Port. Then, log into the router (192.168.50.1). Go to QoS > Adaptive QoS. Ensure "QoS" is toggled ON. Under "Bandwidth Setting," run the speed test to set your baseline. Then, under "QoS Type," select "Gaming." This applies system-wide prioritization for gaming traffic. For more direct control, go to QoS > QoS > "Game" tab and you can manually assign your Xbox's IP address to the highest priority.
IF THAT DIDN'T WORK If other devices are still saturating your upload bandwidth (like someone backing up photos to the cloud), gaming can still lag. Go to QoS > Bandwidth Limiter and set mild upload/download limits on non-critical devices to prevent them from hogging the entire pipe.
HEADS UP QoS, especially Adaptive QoS, adds processing overhead. If you have a gigabit internet connection, enabling it will cap your maximum throughput to around 700-800 Mbps. It's a trade-off for latency control.