I found what is the problem, and why anyone has the solution (the firmware seems to work for everyone without me). I put the solution if it can help a minority as me. In fact, the help guide (with the firmware) and the instructions on the initial topic are good but they remain too vague on the real required specifications.  The cable provided with the monitor has a label where is written "type C gen 2" and it did "tilt" on my mind. My motherboard (Asus Rog Maximus VIII Ranger) was released in August 2015, my computer case is Fractal Define R6 and i have one port USB-C on each other. And it is the motherboard the most important part, because it will only manage the max speed of the USB 3.1 5Gbps (USB 3.1/3.2 Gen 1) for me (my case has a USB-C gen 2). So, USB-C is incomplete as required, the important thing is the standard specification  : USB 3.1/3.2 Gen 2 (Superspeed+) or above WITH a USB-C connector. I updated successfull as Orimm is doing, with a friend's laptop computor. So, if you have a recent computer/motherboard with USB-C, you will never face the problem. I suggest Dell to update the help guide and the firmware notes/application with the real requirements (they just say USB, what is really vague). Have a good day and sorry for disturbing !
Hello! I'm sorry to bump the topic but the Dell_G3223D_FWUpdate_M3C102_Windows.exe (10/10/2022) doesn't work for me (and the back lighting is very annoying feat useless energy consumption). I tried it about few hours with many attempts and it never works. Windows 10 Pro 21H2, GeForce GTX 1060. I try with DP cable provided in the box, with HDMI, with USB-C to USB-C cable provided in the box, with a USB-C to USB-Type A (on the 2 ports, in both ways), with USB-Type A to USB-Type A, antivirus disabled, reboot computer, power on/off the monitor : nothing works.  I'm very disappointed especially after everyone says it works in other thread! Any help possible? The previous firmware M3C102 24N58 isn't available anymore. I can't try it and I can't find it on the internet. I'm available for more information if it can help. Thanks in advance!
G3223D, firmware M3C102 4WW4X, cannot turn off lighting