Thanks for all your replies. Really appreciated.  I have fixed this issue with the following settings. I think it might be some Dell's Windows system issue, or my Windows missed some critical files for some reason. I don't know why this is happening.  You will need one cord mouse and an Internet connection.  First thing first, check the same receiver and devices on another device, to make sure all hardware is fine, and this is only related to Dell's desktop device.  You have a keyboard or mouse that supports the Unifying function. My devices are "M330" and "MX Keys," get Logitech unifying management software available on your device, and install it. If the software saying it cannot detect the receiver, then this is the right for you.  Go to device manager (right-click the Windows icon), under "Mice and other pointing devices", disable all "HID-compliant mouse" devices, not you cannot use your Logitech mouse anymore. Insert the corded mouse, and wait for a response, once the cursor appears, and you are able to control with the corded mouse, unplug the Logitech Unifying receiver.  Wait the Manager windows refreshes, and the device you just disabled is disappeared. Now download this file and install it, [URL] I downloaded it as a reference, if you can find it on your own, please do so, the name of the software is called Logitech SetPoint. This software seems like can fix the missing file in Windows. Just install it, and ignore all messages, such as you don't have compliable devices, etc. After installing, re-plug in the Unifying receiver to one of the USB 3.0 Port, on the backside.  Now reactivate the HID device in the Device Manager. After refreshed, unplug and replug in the USB 3.0 port again. Now Windows should be able to detect this Unifying receiver. Open "Logitech Unifying Software", you will be able to process all the setup steps successfully.  You may uninstall the "SetPoint" afterwards.  This works for me, and I tried to restart the system, everything is good. You can use Logitech Options to customize everything now.  Let me know if this works for you or not! I wish this helps you. 
Logitech Options software cannot recognize the unifying receiver, but the mouse and keyboard work fine. I need Options software to customize keyboard shortcut keys. Here are some screenshots I took when I contacting Logitech support.  The driver for my whole system is up to date. Based on the Dell Support app pre-installed on my computer.  This is in Windows Settings, the receiver saying the driver is unavailable.  [IMAGE] This is a Unifying software Logitech support guy sent me. The computer cannot detect it. So they ask me to check this issue with the manufacturer.  [IMAGE]   This is a screenshot from Logitech Options software. [IMAGE]   This is the device manager screenshot.  [IMAGE]
XPS8940 Logitech Unifying USB receiver cannot be detected