You can place little dots of color on the canvas and then smear it with a smudge engine RGBA-brush, in smearing mode, and color rate set to 0 or unchecked (or with curve controlled by pressure if you wish to blend into a single color).
It’s tricky to get such intricate impasto effects (as shown in the image you linked) only using rgba brushtips. But you can try this template that uses the paint transparency as a height map: Alpha Bumpmap Impasto Template
Colors don’t blend as good however, and it runs quite a bit slower. And it’s only bump and no cast shadows but you could export the height map and render in a 3D software like Blender.
