I think I have faced this issue before, and it seems to be occurring again.
I am trying to search a text Stack text field for a string of text to update.
Either it is greyed out, or when it shows under the menu, nothing happens.
It seems to be confined to text within a Stack.
Or… does find/change simply not work within a text stack?
Nevermind, I found my old support notes for this issue. It seems that find/change does not work within a text stack.