Hello
This sounds more like Windows 11 Presence Sensing than a separate “Monitoring Mode.” On supported PCs, it can automatically turn off or lock the screen when you move away, including when an external monitor is connected.
Go to Settings > System > Power & battery > Screen and sleep, then turn off “Automatically turn off my screen when I leave.”
Also open “More options” and disable “Lock my device when I leave while an external display is connected.”
Microsoft’s official guide: https://support.microsoft.com/en-US/Windows/privacy/managing-presence-sensing-settings-in-windows-11
If those options are not shown, please tell me the PC/monitor brand and model, as some manufacturers control the same feature through their own utility.