I used to be able to "Create a Virtual Copy" - now, even though just one image is selected, I have the option to "Create Virtual Copies" - and every image in my Quick Collection is copied.
I only want to Create (1) Virtual copy!
This seems new with 10.1.1.
A quick test here in both a collection and a folder with 1 image selected on 10.1.1 Mac works for me.
Does restarting help at all?
Are you sure you have only one photo selected? Try Ctrl-D/Cmd-D to deselect, then select one photo and try it again?
I'm using LrC 10.1.1 on a Windows 10 PC. If I highlight a single image and choose to create a virtual copy LrC only creates a virtual copy for that highlighted image. I tried that with a group of images in the Quick Collection.
If all images are selected, there will still be a 'most selected image' that looks different. This can easily fool you into thinking that only this one image is selected.
I ran a quick test and everything works well on my end. Two quick things to consider.
1. Ensure that just one image is selected
2. Have you uninstalled and reinstalled the application?
Like the others before me, I too tested my lightroom 10.1.1 (on a Mac with Catalina) and it works as it should, making only one virtual copy, if one image is selected. And I also tried both from all my images and from the qucik collection.
Try quitting LR, and then launch again to see if it works.