Hi @Alexdici
If you want to use, as your DNS Servers, the one from Google (8.8.8.8) and the one from Quad9 (9.9.9.9), I suggest that you, in that same network setting window that you showed in the screenshot of your post ("Modification de Connexion Ethernet 2" - "Paramètres IPv4" tab), do the following:
1 - Change the selected value in the "Method" ("MĂ©thode") dropdown list from "Automatic (DHCP)" ("Automatique (DHCP)") to "Automatic (DHCP) addresses only" (I don't know what is the French translation but it should be the second option in that "MĂ©thode" dropdown list).
2 - In that same window, add the Google and Quad9 IP addresses of their DNS Servers in the "Serveurs DNS supplémentaires" ("Additional DNS Servers") text box (which will have its description changed to "Serveurs DNS" / "DNS Servers" by then): 8.8.8.8, 9.9.9.9
3 - Also in that same window, click on the "Enregistrer" button (in the lower right corner) to save your changes.
I hope that helps. Please reply later to say if doing that solved your issue (or not)