You can configure a string-type flex field as a drop-down list or a lookup field to enable easy data entry, reduce user error, and speed up filter search. For example to be able to filter for highly fragile content, you could create a list with the following values: high, medium, low, and none.
To implement a list of values (LOV), you can:
Specify a list of values to appear in a drop-down list for a flex field (on page 1) in the Edit Metafield form
Include a system-defined LOV (on page 1) when overriding a variform
Specify a simple LOV (on page 1) driven by an entity query
Use a code extension (on page 1) to implement a list of values (pick list)
For more information, see Use flex fields (on page 1).