This reminds me of the failed MFbar on the EOS R.
It may be even worse, because there may be no other dial left for easy exposure compensation if you feel forced to disable it.
I must say it's the first time I feel so "held back" by a feature.
I'm waiting for the user manual to see if it can be combined with held m-Fn button (or anything else) to lock/unlock it at will.
It could be ok in the field as we don't need to have unwilled exposure changes to interfere, but still, you'd be losing one button for this purpose.
But still, there is another point that is more important to me and it's the prominent shape of the "housing" of this dial : for instance, I love the way you can easily change mode with thumb on R6. This dial shaping out up of the body probably prevents from being able to do so. I bet this shape can be uncomfortable for other reasons when camera is in hand. However, a real test in the field is needed to figure this out.
At first sight at least, it really looks like ergonomists at Canon missed things (or just tried without thinking at least twice)... why didn't they simply keep the ergonomics of the R6? Adding the Iso button is a good thing though but it could have been done with R6 ergonomics as well (and would probably have been enough to have it done the right way).
Also, adding the MF/AF switch looks a bit "outdated" to me. On Nikon DSLRs I sometimes felt like using it with older AF-D lenses that can't override AF, but never with modern lenses. But maybe there could be other usages I miss. It's true that some lenses protections can hinder easy access to AM-MF button on the lens.
At this right point, this announcement and specs make me think we're more in need of a R6/R5 firmware update that adds "any starting boxe shapes" ability on tracking AF, as in the R3 and in these two new models.