You can find this effect in the Toolbox under the objects tab, in the live effects section.

The mosaic effect creates a pixelated effect in your images, and you can adjust the size of the squares yourself.
There are three variants:

•Mosaic

•Circle mosaic

•Shape mosaic

Insert Mosaic effect

To use the effect, you can drag it directly onto an image in the Timeline.

You can also drag the effect to the Timeline and insert one or more images later.

If you click on the colored frame, you can specify the settings for the effect in the Properties area.

In the Properties window you can make the following settings for the Mosaic effect and the Circle Mosaic effect:

•Number of rectangles or circles  and rotation of rectangles

•Width, color and Smooth border

Shape mosaic settings

In the Properties window you can make the following settings for the Shape Mosaic effect:

•Shape

•Number, rotation and size of the selected shape

•Background color and Smooth border