Check this out from photography life .com I happen to like vignetting myself. I often add it. The corners, to me, are not bad at all on a well lit subject. Outdoors it is barely visible. They are far from straight up black. I should add that I never take photos of just walls and backdrops... solid color or brick. I have seen tests that give the wide open vignetting anywhere from 3 to 4 stops. I personally think that 4 stops is a real stretch and how the backdrop was lit will contribute greatly as to the test results. In camera auto correction makes it a non-issue. Then the vignette is almost gone by f/1.6.
Ultra-wide aperture lenses usually produce heavy vignetting, and the RF 50mm f/1.2L USM exhibits around 3.3 stops of light falloff at f/1.2.
Canon EOS R + RF50mm F1.2 L USM @ 50mm, ISO 100, 1/8000, f/1.2
Things improve at f/1.6, where vignetting is only about 2.2 stops, better than many wide-aperture lenses on the market. By f/2, vignetting is easily correctable (about 1.5 stops) – and it is a non-issue at f/2.8, totaling only one stop. Beyond that, the RF 50mm f/1.2 exhibits less than a stop of vignetting, which is negligible in real-world images.
Canon EOS R + RF50mm F1.2 L USM @ 50mm, ISO 100, 1/1600, f/2.8
Then there's this: https://www.opticallimits.com/canon_eos_ff/1055-canonrf50f12?start=1
I don't mind some slight vignetting either.
But, remember when you correct for 1.5 stops of vignetting in the corner, you're losing 1.5 stops of DR in those spots. Depending on you use case that may be an issue.