3.27 How to make Maple display diff(y(x),x) as y’(x) or as y’ ?

Add this

expr:=diff(y(x),x); 
Typesetting:-Settings(typesetprime=true, prime=x):
 

The above will display the expression as \(y'(x)\). To make it now show the \(x\) do

expr:=diff(y(x),x); 
Typesetting:-Settings(typesetprime=true, prime=x): 
Typesetting:-Suppress(y(x));
 

Now it will show the expression as just \(y'\). For all the above to work, make sure you have Typesetting level set to Extended in the GUI.

This is done inside Tools->Options->Display menu.

To clear all the above Typesetting, do restart or do Typesetting:-Unsuppress(y(x))