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.
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.