Sidecar not working.

Hello, so my father has a 2014 Macbook Air that he just recently updated to macOS Catalina. He updated only for the sidecar feature, due to the fact that he has a 2018 iPad Pro. But he was dissapointed to find out it did not work. Here is what he did :

-Both the Macbook and the iPad we're connected to the same network

-Both had AirPlay turned on, so did they have Bluetooth.

-He opened his AirPlay and the iPad just -wasn't there.

-He then read the manual for sidecar and noticed that it had to be turned on in the system preferences, but when he opened them ; there just wasn't an option for it, nor it the search bar.

Please help me fix this problem, thanks in advance!