P: Library zoomed view shows wrong color

no, same issue with sRGB still.

My son is using sRGB, perhaps that's the difference? 

As me and many others have this issue and can easily reproduce it - I again rechecked also with AdobeRGB default profile, with internal MBP display, with/without GPU, for different camera brands- and as it might be not very obvious depending on the object color nature but clearly visible in comparison of the library vs. develop zoomed image, may I ask you to provide some screenshots of the same image in lib/dev mode fit screen/zoomed view? I can also share an example image to compare the result on my / your sons system. I would appreciate to see that there are systems out there with latest LR / MacOs who don't show this bug which many of us annoys. 

My son doesn't have this problem on either a MacBook Pro 16 or a MacBook M1 16gb. Same for the laptop displays and a 4k external Dell monitor. So it could be a setting difference. He is using the latest versions of macOS and Lightroom with no add-ins for either. Both are uncalibrated with the Apple profiles. 

Aside, he does not have any of the other problems reported on this forum other than slow scrolling in the Library module which has existed in every version of Lightroom.

I can well imaging that a SW with thousands of features and hundreds of different HW deployments it needs to run on makes it difficult to detect such a bug. Still, for Mac users it seems to be easily reproducible at least maybe for those applying color management. So I would not consider it "extremely rare". Or are there Mac users with LR10.1.1 on Big Sur who do not see this issue?

No, none of Adobe’s testers myself included discovered the big, it's extremely rare.

Adobe again displayed total lack of quality control and unimaginable levels of sloppiness while releasing their software. Such a bug should never be allowed in release since it is plainly reproducible within 1-2 clicks of any standard workflow in LR!!!

All Macs on Big Sur are affected

I just changed from Windows PC to Apple MacBook Pro M1, when I noticed same issue. In library mode zooming the saturation changed significantly, no matter what kind of picture (raw,jpg...) As I tried on my windows PC with latest LRC version no problem at all. Then I tried LR und PS, zooming a picture with no such bug whatsoever.

Attached are a couple screenshots showing the difference.