Is the Canon RF 28mm F2.8 STM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 28mm f/2.8 test image. Observe the contrast and resolution of these results.
Is the Canon RF 28mm F2.8 STM Lens set to 28mm f/2.8 sharper than the Canon RF 24mm F1.8 Macro IS STM Lens set to 24mm f/1.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.