Cortana's lock screen usefulness is limited & often distracting. If you want to, here's a way to disable Cortana on Windows 10 lock screen.
Microsoft shoehorned Cornata into Windows 10 and dreamed of people using the virtual assistant for performing all kinds of Windows functions. However, it proved to be too much even for Microsoft. For the most part, Cortana only does pretty basic stuff like setting alarms and showing weather info. If you want to do something worthwhile like opening a file or program, you have to do it manually. Simply put, I've never seen people using Cortana for anything other than for amusement.
Having said that, I don't understand the Cortana's place on the lock screen. Sure, while on the lock screen, Cortana can do basic things like showing notifications, change track or volume, etc. However, most of us never use these features because we are not even in front of the system while it is locked.
So, if you are like me who doesn't like having Cortana on lock screen in Windows 10, follow the below steps to remove it.
1] Disable Cortana on Lock Screen from Settings App
Fortunately, you can disable Cortana directly from the Settings app. All you have to do is toggle a switch and you are done.
1. First, open the Settings app by searching for it in the Start Menu or by clicking the "All Settings" button in the Action Center. Alternatively, you can also press the Win + I keyboard shortcut. After opening, go to the "Cortana → Talk to Cortana" page.
2. On the right panel, toggle the switch under "Use Cortana even when my device is locked" to the "Off" position.
That is all, you've disabled Cortana on the lock screen. There is no need to restart the system.
Do keep in mind that the setting is applicable to your user account only. Other users on your system can still use Cortana on the lock screen. If you want to disable Cortana on the lock screen for all users then I recommend you follow the second method.
2] Cortana Lock Screen GPO
If you are looking to disable Cortana for all users then you can use a Group Policy Object. We just have a configure a single Group Policy and Cortana on the lock screen will be disabled.
1. Open Group Policy Editor by searching for "Edit Group Policy" in the start menu. After opening the GP Editor, go to the following location by expanding the folder structure on the left panel.
Computer Configuration → Administrative Templates → Windows Components → Search
2. You will see a bunch of policies on the right panel. From that list, find and double-click on the "Allow Cortana above lock screen" policy.
3. As soon as you double-click the policy, the policy configuration window will open. Here, select the "Disabled" radio option. To save the changes, click on the "Apply" and "Ok" buttons.
4. Finally, reboot the system or execute
gpupdate /force command in the elevated Command Prompt window to apply the saved changes.
That is all. If you want to revert the changes you just made, i.e, enable Cortana on the lock screen, go through the process again and select "Not configured" or "Enabled" radio option in step 3.
I hope that helps. If you are stuck or need some help, comment below and I will try to help as much as possible.