Shootout @ 12mm: Sony FE 12-24mm f/2.8 GM vs Sony FE 12-24mm f/4 G: Two Aspen
See my Sony mirrorless wishlist.
Compared here on the 60-megapixel Sony A7R IV are the Sony FE 12-24mm f/2.8 GM to its Sony FE 12-24mm f/4 G sibling. What do you get for your money, besides an extra stop of lens speed?
Shootout: Sony FE 12-24mm f/2.8 GM vs Sony FE 12-24mm f/4 G: Two Aspen
Includes images at up to full camera resolution from f/2.8 through f/13 with extensive crops and analysis.
The about $2998 Sony FE 12-24mm f/2.8 GM is surely the best zoom lens of its kind ever produced.

Sony A7R IV + Sony FE 12-24mm f/2.8 GM @ 12mm
ENV: Lundy Canyon, altitude 8050 ft / 2454 m, 28°F / -2°C
RAW: LACA corrected, vignetting corrected, push 0.66 stops, +20 Shadows, -87 Highlights, +30 Whites, Color Luminance {Greens +50, Yellows +20}, +15 Clarity, USM {7,50,0}
[low-res image for bot]