After transferring a catalog and all of the picture files to an external drive, all stacks are expanded and the stacking sub menu is greyed out. What has happened?

Please post a screenshot of your entire screen. Do not cut anything off.

No satisfactory answer.

Yes, I did “find missing folder”.

Just to get this out of the way: when you “showed it where” the local picture files are, this was done by “Find Missing Folder” - not by Import? In the latter case: prior editing History would not show for these photos even if their latest editing does; and nor would any virtual organisational attributes, such as Collections but also ‘stacking’. Any Virtual / Proofing Copies previously made, would be absent too.

Agreed that it matters anyway about 1) single or multiple selected image(s); 2) whether you are in a Smart Collection based view.

That still does not make it clear where you are when you see this problem. Do you see it in ‘All Photographs’? Is that what you are saying? Do you have at least one image selected?

This is the entirety of 6 months worth of photos.  I don’t use collections.

Are you perhaps in a smart collection? Smart collections do not support stacks, so the stacking submenus are all dimmed.