How to enable expressions in kibana[7.3.1] for scripted fields

I was trying to setup a scripted field in kibana. I wanted to use the expression language ( as shown in this video from elastic: https://www.youtube.com/watch?v=BhmpDtS7g28) but I only have an option for painless. Is there a way to install/enable the expression language? alternatively is there a good place to see some examples of painless in use? In my experience with it it has been anything but.

We only provide an expression editor in Canvas for now- while the language does internally power a lot of Kibana, and you could build Kibana plugins that interact with it, it's not yet user-facing outside Canvas.