I have a Moto G4 plus, and I don't see a way to Deactivate the Google app in my home screen (far-left screen).
I have the last Android update installed.
Also, it would be great if I also could get rid of the Google search bar (in order to use duck duck go, for example).
That's how the stock Google launcher is designed (to get to search quickly). You cannot change it.
Also you cannot disable the Google app as it is a system app like @Tinkerbell91 said. But you can try something - uninstall the updates for Google app and there are chances that you can see the Disable button. I've done that before and it worked. BTW I got the same mobile.
Regarding the Home screen use can use other launchers from Play Store. I use Nova Launcher which is very close to stock launcher and provides you to customize the appearance. That is my choice but you got numerous options out there.
That might be apart of your launcher. If it's not you'll have to be rooted because the app is a system app. But, removing it can cause problems such as bootloops so be very careful.
