P: Library zoomed view shows wrong color

@colin_judge I have exactly the same issue here.

Mac OS Big Sur last update
LR last update

Here is the picture in library "adapt"

Here is the 100% in library 

here is the picture in develop 100%

As you can see the 100 % library doesn't match.

I am also experiencing this bug, on a 2020 M1 Macbook Air, both on the built in display and also now on an external display I just received today. The issues is not to do with monitor calibration, it's definitely a bug in the Lightroom Classic Library module. Zooming the image to any zoom level that is tighter than "fit" results in a major colour shift.

This only appears to be an issue in the Library previews, all exported images are rendered correctly. But it makes the Library Module almost unusable for image reviews, as I need to switch to the Develop module in order to maintain correct colours while viewing zoomed images.

I have tried Discarding 1:1 Previews, and then rebuilding them. I have also tried turning off GPU Acceleration. Neither solves this issue.

I never noticed this behaviour until recently, so it was either the 10.1 update, or Big Sur that caused this, can't be sure which.

It's just odd none got transported to the DNG when I imported the DNG. 

I have used "Adobe Vivid" for the example, but I tested with various camera profiles incl. the "Camera Matching" and also some created with xRite Passport Checker.

Got it, still shows the wrong camera profile both in LR and ACR as seen below.

What DCP camera profile are you using on your end? 

here you are: https://www.dropbox.com/s/t272b20mz5p8ica/SK-20201205-210220-CanonEOS5DMarkIV.dng?dl=0

So I tested this again and for some reason, when I imported your raw, despite not using a preset for import, your raw came in with my 5DCopySetup dcp profile. That's odd because my camera differs from yours. That alone might indicate a bug or issue. 

I then assigned Adobe Color. The difference I see between Library and Develop are super tiny unlike my first test. Ditto with Adobe Standard. Zooming in and out in all modules appears the same too. 

What camera profile was originally used? 

Can you convert the CR2 to DNG with any/all settings you had that produced an issue and upload that. The profile you used should be provided within that DNG. 

Ha, I found a way to temporarily switch of the bug:

precondition: apply treatment profile "Adobe Vivid", zoom into image and toggle between Library and Develop, system shows color change.

now do the following: 

1. change vibrance slider to another position

2. toggle between Library and Develop

--> no color change !! only small difference in kind of smoothing/interpolation applied

3. either zoom in/out or pan the image

4. toggle Library/Develop

--> again color change is showing up

Yes, I switched also to standard display profiles by Mac, not created with BenQ software. Same issue.  

I just noticed that the level of difference depends on the treatment profile applied. For Adobe Vivid the mismatch is much more prominent than for others.

As mentioned before, it seems to be the same bug as described here: https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-100-using-the-zoom-to-fill-function-in-the-print-module-shows-the-original-unedited-version-of-the-photo/5fc297e6ecf16939894a4edf.

I can confirm that this bug was not showing up in V10.0. I was trying to check another issue (https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-images-not-sharp-unless-i-zoom-in-and-out/5f5f45fa4b561a3d426c4ceb) which btw. has been fixed with V10.1 for me.