Screenshot Preview Placement In Illustrator (Mac OS) changes document color profile
When taking a screenshot on a Mac (Big Sur, 11.7) a small preview of the screenshot appears in the bottom right corner of the screen. If you grab that preview before it disappears, you can place it in an email, chat app, or any other software that will accept it, including Illustrator and Photoshop. It's a nice little time-saver. However, when I grab that preview and place it in Illustrator, the document becomes either "Untagged CMYK" or "Display" (RGB) on its own. I didn't notice this for a very long time, but was constantly having color problems, only to find out my color mode had been changed without my knowledge to "Display" or "Untagged CMYK". Now I know what's causing it at least! I can work around this of course, but since probably many others are having this problem and don't even know it, I thought I'd pass this on.
Once the color profile is changed to "display" or "untagged CMYK" in this manner, no amount of "Command+Z" will bring back the colors you had OR change the color profile back to the original.
One note: if the screenshot preview is left alone, it disappears and then is saved on the hard drive as a PNG; whereas, if left so save to the hard drive, it is saved as a PNG. If the screenshot is placed conventionally (either dragging from the finder into a document, or via File > Place, this color space change doesn't seem to be an issue. It is ONLY when grabbing the preview to place the screenshot as far as I can tell.

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Russ Gray commented
I just updated this morning to 27.0. The problem persists. I suspect thousands of people are dealing with this every day, and like me for so long, don't even realize it's happening. This needs some attention!