I recall something weird happening when trying to drag the Downloads folder from the sidebar of Finder to the dock, and that I had to go to my home folder, and drag it from there to the dock.
Don’t remember what exactly was weird about it.
Thanks for the suggestions. Unfortunately, the Dock is still dead.
First, this has been a problem with Downloads in the Dock since I first booted the new laptop. As noted above, however, I have deleted the Downloads folder from the Dock several times and re-added it. To no avail.
Secondly, restarting hasn’t changed the behaviour.
Thirdly, dragging the Downloads folder from my Home folder, I noticed it has the little curly arrow badge, even in my home folder. I think that means it is an alias. Is that right and, if so, why would that be?
I suspect Finder wants the Downloads folder to stay where it is.
However, I see no reason you shouldn’t be able to add Downloads to the dock. The only thing I can think of is that folders have to be on the right side of the dock - to the left of the Trash icon.