Right click on the Network Manager Icon - select "Edit Connections".
Select the connection - click on the "Gear" icon.
In the "Editing" window, go to the General Tab, and deselect "Connect
Automatically".
Thanks for your answer, but can I configure the network manager to prevent it from connecting to any new free Wi-Fi or previously used ones? If I go to a place with many free Wi-Fi spots, I want to choose which one I want to connect to. If, for some reason, the connection is down, I want to be able to choose another Wi-Fi network. I don’t want to automatically connect to a free Wi-Fi network without my observation.
If you're using a disposable sys-net in Qubes, this feature should already be effectively disabled. However, you can also manually uncheck the "connect automatically" option in NetworkManager. Qubes does not automatically connect to open WiFi networks, so you shouldn't be experiencing that.
Right click on the Network Manager Icon - select "Edit Connections".
Select the connection - click on the "Gear" icon.
In the "Editing" window, go to the General Tab, and deselect "Connect
Automatically".