Is the Canon RF 600mm F11 IS STM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 1200mm f/22.0 test image. Observe the contrast and resolution of these results.
Is the Canon RF 600mm F11 IS STM Lens set to 1200mm f/22.0 sharper than the Sigma 60-600mm f/4.5-6.3 DG OS HSM Sports Lens set to 600mm f/11.0? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.