Copy to selected not available or doesn't work when highlighted Having problems with copy to selected across the board. 
I'm trying to add a modifier to all selected objects. It's Greyed out.
They are meshes in their own collection, no other objects.

(skip to the end for main question)
Yesterday, I was selecting all objects and trying to add a material.
Copy to selected was available but wouldn't do anything.
I had to join every object and then separate (which isn't the worst),
but the objects were tied to shrink-wrap and probably had to use copy to selected to get them working again...

How do I add a modifier to All selected objects?
Select all your objects, then at last Shift select the one with the modifier, then ctrlL > Modifiers. By the menu bar: Object > Make Links > Modifiers.