Perhaps I can upload a couple of examples laterOptical limits found 3.24 ev at f/1.2: "Ultra-high speed lenses produce quite some vignetting on full format sensors and the RF 50mm f/1.2 USM L is no exception to the rule here. At f/1.2 the vignetting exceeds 3EV (f-stops) which is, of course, easily visible. For some this may be an issue whereas others may actually prefer such an effect. Stopping down to f/1.6 and, more so, to f/2 reduces the issue substantially albeit there's still some light falloff visible. Traces remain at f/4 and beyond." https://www.opticallimits.com/canon_eos_ff/1055-canonrf50f12?start=1
I can't see any real problem either.