Yes—diffraction is a real issue in macro photography, but the tradeoff is different from normal-distance shooting. At macro distances, depth of field becomes extremely shallow, so stopping down to a very small aperture can add enough usable depth of field that the overall image looks better, even though the exact plane of focus becomes softer from diffraction.

In other words, diffraction still happens, but in macro work the gain in depth of field often matters more than the loss in peak sharpness. That’s why macro photographers commonly use small apertures, especially with flash to compensate for the reduced light.

So it is something to be aware of, but not necessarily something to avoid at all costs. In macro photography, the “best” aperture is often the one that gives the best balance between depth of field and diffraction for your subject.