Dell UltraSharp U3821DW User Manual page 62

If either USB Type-C, DisplayPort, or HDMI input is selected and the corresponding
cable is not connected, the following message will appear:
NOTE: The message may be slightly different according to the
connected input signal.
When the monitor is under DP/HDMI input and a USB Type-C cable is connected to
a notebook that supports DP Alternate Mode, if
the following message appears:
You will see the following message before the Lock function is activated:
NOTE: The message may be slightly different according to the selected
settings.
│
62 Operating the monitor
Auto Select for USB-C is enabled,