Normally, you can drag a collapsed stack from one folder in the Folders panel to another, and all stacked photos will be moved, including any virtual copies inside the stack. But if a virtual copy is on the stack top, you'll get an error message.
1. Make a folder F1 containing pics A, B, C, and D.
2. Stack A on top of B. Make a virtual copy of C and stack it below C. Make a virtual copy of D and stack it on top of D:
3. Collapse all three stacks.
4. Drag the stack with A to another folder. Drag the stack with C to another folder. Both moves succeed.
5. Drag the stack with the virtual copy of D on top to another folder and observe this incorrect error message:
The error message is incorrect on two counts: First, the original file is selected (just as the photos in the collapsed stacks in step 4 were also selected). Second, virtual copies can be moved to another folder (as in step 4.)
6. Expand the stack with D, select both photos, and drag them successfully to another folder.
When I try to move a stack (from one folder to another) where the top image is a virtual copy of another image in the stack, I get the message "Cannot move files. All of the selected images are virtual copies." In order to move the stack I have to make a different image the top image in the stack, then move it, then move the images back to the correct order. This error has been around for quite a few versions and persists in V12 (Mac, M1).