Disable WiFi on Ubuntu:
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Note: you will need the network-manager package installed.

To disable WiFi on Ubuntu in CLI:
sudo nmcli radio wifi off

To turn it back on:
sudo nmcli radio wifi on

To get help:
sudo nmcli radio help

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Source: https://www.ubuntupit.com/how-to-disable-wifi-on-linux-system-gui-and-cli-methods/
Date: April 1st, 2021