U2720Q, two laptops, USB usage?

@ttimt  The only way to create a USB data path between the display and source PC is to use the USB-C input port, which means there's no way to have two source systems connected simultaneously such that each one has a USB data path to the display -- not even in an "active/passive" mode that allows you to toggle.  Dell has some displays that offer multiple USB host ports, but this is not one of them.  For this display, if your system has a USB-C port, then a regular USB-C cable between the display and PC will allow you to run video, USB data, and power all over that cable -- assuming your system's USB-C port supports all of those things, of course, which not all systems with USB-C ports do.  You also need a USB-C cable that supports all of those things, and not all USB-C cables do either.  Otherwise, you can use a USB-C to USB-A cable to connect the display's USB-C input port to a USB-A port on the system, in which case you'll just have a USB data path, with no video from the system or power flowing into the system.  You could also use a USB-C cable with a female USB-C to male USB-A adapter to plug into the system's USB-A port, but whichever method you choose, make sure your cable anda adapter if applicable both support USB 3.1 Gen 1.  Some USB-C cables, C to A cables, and C to A adapters only support USB 2.0.

Also note that you cannot use the downstream USB-C port on the side of the display to connect to a system.  A downstream port is meant for USB-C peripherals, not for a connection to a USB host device like a PC; that requires an upstream port, and the only upstream USB port on this display is its USB-C input port.

@Akimoto747  If you want the USB ports built into the display to be usable from the attached system, you have to connect the display to the system in one of these ways:

• If your system has a USB-C port, get a regular USB-C cable that supports at least USB 3.1 Gen 1 (some only support USB 2.0) and connect the display's USB-C input to the USB-C port on your system.  If your system's USB-C port also supports video output, then you'll have video and USB data running over that single cable.  If it doesn't, then you'll need to make some other connection for video output.
• If your system doesn't have a USB-C port, then get a USB-C to USB-A cable that supports at least USB 3.1 Gen 1 (again, some only support USB 2.0) and connect the USB-C input on the display to a USB-A port on your system.  Then you'll need to use a separate cable for video.