This parameter controls the layer visibility (it is more like an alpha value).
0 means the layer is invisible,
1 means the layer is visible.
How to show or hide a layer, or fade the effect of a blur?
In the Parameters Panel, look for an option
Opacity - this controls how much of the
blended result of the layer is composited with the blend of the layers
In other words, for a typical layer, this will ‘fade it out’. For a Blur Layer set to “Blend Method: Straight”, this will fade between the blurred version and the unblurred version of the canvas. If you want it to become less blurry, adjust the Blur Layer: Size.
If you want to affect multiple layers at the same time, you have several options:
You can Group Layer your layers and use the group’s Opacity Parameter,