DIAGNOSIS: The USB hub built into the monitor needs to be activated by connecting the upstream USB-B cable from the monitor to your computer. It doesn't get power or data from the HDMI/DisplayPort cable alone.
FIX: Locate the square-shaped USB-B port on the back of the monitor (next to the HDMI/DP ports). Connect the included USB upstream cable (looks like a printer cable) from that port to a standard USB-A port on your computer. Once your computer is on and the monitor is displaying an image, the side USB ports should now provide power and data.
IF THAT DIDN'T WORK: The USB upstream port on your PC might not be providing enough power. Try a different USB port on your computer, preferably one directly on the motherboard (back of the PC) rather than on a front panel or hub. Also, check the OSD menu under USB Settings to ensure the hub isn't set to a sleep mode.
HEADS UP: These are USB 3.2 Gen 1 ports (formerly USB 3.0). They're fine for peripherals, storage, or charging, but don't expect super high-speed data transfers compared to a direct motherboard port. Also, they only work when the monitor is on and connected to an active source.