The last and most important mode, ‘Extend’ lets you extend your actual working area to the second monitor. The dual monitor setup is essentially about working in this mode on your computer.

Like its predecessor, the 491CQP, the new 491CQPX variant employs a curved QD-OLED panel with the same Dual-QHD resolution, ...

They then often opt for a dual monitor setup or even a multi-monitor setup. However, when you use a dual monitor setup, it is quite difficult to use a single wallpaper on both of the monitors.