Unable to connect MacBook Air as second display for iMac

I currently have the 2017 iMac and recently purchased the 2020 MacBook Air.

Now I'm trying to connect the MacBook to my iMac so I can use it as a second display.

I already read the support page about connecting multiple displays, but it's not working.

Made sure they both supported the thunderbolt 3 cord and purchased one.

Plugged it into the ports on each computer - the MacBook even shows that its plugged in and charging

Went to System Preferences > Displays, but there is no "Arrangements" tab for me to select

Pressed the Option key and clicked on Detect Displays, nothing happened.

I don't know why it's not working or what else I am supposed to do.