The only solution that worked for me:
1/
Download "Realtek HD Audio Manager" https://www.realtek.com/en/component/zoo/category/pc-audio-codecs-high-definition-audio-codecs-softw...
2/
Start Dell Audio "RtkNGUI64.exe" in C:\Windows\System32\DriverStore\FileRepository\hdxrt.inf_amd64_b0026a592e9b4de4
3/
Select the last tab (advanced)
Select Plug info
Click on the radio button with no name
Select the right device (headset with mic)
From time to time (each restart or OS update?), you will have to start-over to point 2. This is why I put a shortcut on my desktop to the Dell Audio program...
French screen-shot:

Source:
https://www.dell.com/community/XPS/Impossible-de-brancher-un-microphone-via-la-prise-jack/td-p/7787363