Why does my monitor keep dimming?

If it is possible to set the brightness of your screen, it will dim when the computer is idle in order to save power.

When you start using the computer again, the screen will brighten.

To stop the screen from dimming itself: Switch Dim screen when inactive to OFF in the Power Saving section.

How do I stop my screen from dimming Windows 10?

Go to Control Panel, Hardware and Sound, Power Options. Click on Change plan settings next to your active power plan. Click on Change advanced power settings. Scroll down to Display, then under Enable adaptive brightness, switch it off for both the battery and plugged in modes.