Sometimes enabling the Particle Background does not change anything in the background. This might happen because widgets are covering the entire row/column and there is no space for particles background to show up.
For example – In a row, you have added a heading and added a spacer above and below the heading. Consider you applied a background color for all these widgets. This will occupy the entire space in the row. So particle background added to row will not display as it has heading and spacer above it. In case columns or widgets have a transparent background, particles background will be visible.
To solve this make sure to set a transparent background to all columns/widgets that display above the row where particles background is enabled.