can't change "Zoom in" shortcut in InDesign

Hi dear all,

I am working with the latest version of InDesign. I was trying to change the shortcut for "Zoom in" from Cmd + = (which is impossible to work with if you are on a German keyboard) to Cmd +, to fit all other Adobe programs. Unfortunately, the program won't let me assign the Cmd++ + shortcut as a new shortcut for "Zoom in". I tried to assign Cmd for any other empty shortcut and it wasn't working either, neither when I tried to assign something with Shift + or Option + or Command + ...

Can anyone help me with this?

Thank you.