Is the Sony FE 12-24mm F4 G Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 12mm f/4.0 test image. Observe the contrast and resolution of these results.
Is the Sony FE 12-24mm F4 G Lens set to 12mm f/4.0 sharper than the Sony FE 12-24mm F2.8 GM Lens set to 12mm f/2.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.