Shortcut of zooming out in Windows in Parallels Desktop
Per Google, it is Control++ to zoom in and Control+- to zoom out on a French keyboard.

I'm not sure exactly which shortcut you're referring to since there's multiple zooms (12 by my count), but a full list of French shortcuts can be found here.

It's possible that your keyboard layout is misconfigured. Ensure it's properly configured by performing the following steps:


  
  Click on the Start Menu.
  Click on Settings.
  Click on Time &amp; language.
  Click on Region &amp; language.
  Click on the language you wish to add a keyboard layout to.
  Click on Options.
  Click on Add a keyboard.
  Click on the keyboard you want to add.