Diagnosis
The KVM peripheral switching function is not activating. This is usually a cable or software configuration issue, not a hardware fault.
How to Fix It
First, confirm the physical connections. The PC you want to control must be connected to the monitor's designated upstream port: USB-C (for video and data) or USB-B (for data only). Your keyboard and mouse must be plugged into the monitor's yellow-marked KVM USB ports, not the standard black USB ports. Use the OSD Sidekick software or the monitor's physical KVM hotkey to switch, not just the input source button.
If That Didn't Work
Install the latest OSD Sidekick software from Gigabyte's support page for the M27Q X. The software manages KVM profiles. Reinstall the monitor's USB drivers in Windows Device Manager after a fresh software install.
Heads Up
The KVM function requires the monitor to be the USB hub for your peripherals. If your keyboard/mouse software (e.g., iCUE, Logitech G Hub) is running, it may conflict. Try closing that software before switching.