For reasons only known to Microsoft since the AU update you can no longer disable it from the desktop. However you can make the following registry change to work round this.
Press Windows+R and run “regedit” and navigate to the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\Windows Search
If you don’t see a “Windows Search” below the Windows folder, right-click the Windows folder and select New > Key and name it “Windows Search”. Right-click the “Windows Search” key (folder) and select New >