GoKawiilA monitor with a USB hub has two sides to the connection. The upstream port, which sends data from the monitor to your computer, connects the hub to the PC. The downstream ports, which send data from connected devices into the hub, are where you plug in accessories such as a mouse, keyboard or flash drive. Data from those devices travels through the monitor and then reaches the computer over the upstream connection.
There's no rule that a monitor with two visible USB ports must have one upstream and one downstream port. For example, a model might have two downstream USB-A ports and a separate USB-B upstream port, while another may use USB-C for its upstream connection. The labels or manual should show how the ports on a given monitor are assigned.
That upstream connection is easy to overlook if the monitor connects over HDMI or DisplayPort. A standard HDMI or DisplayPort cable doesn't provide the USB data path that the hub needs, so monitors that use those video connections need a separate USB upstream cable for their downstream ports to work.
USB-C can combine those jobs when the hardware supports it. DisplayPort Alt Mode allows a compatible USB-C connection to carry video alongside data, while USB Power Delivery can add laptop charging. USB-C itself only describes the connector, however. Support for standards such as USB 3.2, USB4 and USB Power Delivery varies by device. That's one reason the differences between HDMI, USB-C and DisplayPort extend beyond which connector fits your computer.