Solved! Pixel 3 doesn't allow to switch the control from "This phone" to "Connected device".

[y2016new]

I need to use on my PC an application which assists with Android phones. For that the application requires that the phone will allow the PC to take the control on the phone. But in the phone, under "USB Preferences", my Google Pixel 3 doesn't allow to switch the control from "This phone" to "Connected device". When trying to switch the control, after few seconds it gives a line saying, "It Cannot be Switched".

How can I make the Pixel 3 to allow it ?

The phone is allowing to transfer files from the phone to the PC with USB cable, but not allowing the control switching.

 

[y2016new]

I need to use on my PC an application which assists with Android phones. For that the application requires that the phone will allow the PC to take the control on the phone. But in the phone, under "USB Preferences", my Google Pixel 3 doesn't allow to switch the control from "This phone" to "Connected device". When trying to switch the control, after few seconds it gives a line saying, "It Cannot be Switched".

How can I make the Pixel 3 to allow it ?

The phone is allowing to transfer files from the phone to the PC with USB cable, but not allowing the control switching.

I have found the answer, you need to enable developer mode.