I met many times that very often  wifi hot switcher  (fn+f9) in  Ubuntu doesn't work.  Usually it brings enough pain for people.  Some time I suffered too. Until today.

I wrote a simple script - a wrapper for rfkill.

It safes time, you can bind it to fn+f9 keys via gnome-control-center -> keyboard -> shortcuts

source code: wifi_switcher.py

requirement:

python and rfkill utility