Dell UltraSharp 34 User Manual page 50

USB Allows you to assign the USB upstream port for the
input signals (DP, HDMI 1, and HDMI 2), thus the
monitor's USB downstream port (eg. keyboard and
mouse) can be used by the current input signals
when you connect a computer to either one of the
upstream ports. See also Setting the KVM switch
for details.
When you use only one upstream port, the
connected upstream port is active.
NOTE: To prevent data damage or loss, before
changing USB upstream ports, make sure that NO
USB storage devices are in use by the computer
connected to the monitor's USB downstream port.
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50 Operating the monitor