"Code Expression" for calculations not available

Hi there, I am just starting with FF and following a step-by-step tutorial that ultimately leads to using "code expression" (in Value Set) in the Action Section of a Button Widget.

Yet, "code expression" just doesn't show up. There is a "custom code expression" (for paid plans; I am on a free plan for testing FF).

Isn't "code expression" no longer available, and is it just "custom code expression" when having a paid plan?

Thanks!