Hello,
I finally managed to correctly configure my mac mini mi-2011 , thanks to the advice of the forum.
Three screens activated
1 HDMI output
1 displayport output
1 USB 2.0 display adapter / HDMI output (WAVLINK)
https://imagizer.imageshack.com/img923/7857/UjVu9s.jpg
https://imagizer.imageshack.com/img922/9420/PuTPcJ.jpg