You can change the transparency of part of an object by using brushstrokes. You can change the nib shape, the nib size, and the opacity of the brushstroke.
You can quickly choose a square or round brush shape by clicking the Round nib button or the Square nib button on the property bar.
The features documented in the Help are available in the full version of CorelDRAW Graphics Suite 2021. Some features may not be available in this version of the product.