When you plug the phone in, you are given options for the "USB connection method".
You must select Internet connection
or Send Images (PTP)
from the list in order to use USB Debugging tools.
For selecting Internet Connection
, the other options sometimes include Charge phone
, Media sync
, and Camera
.
For selecting Send Images (PTP)
, the other options sometimes include Charge Phone
and Media Device (MTP)
.