I've tried to create data object that contains a List filed. But I can't find a way to specify a list of values in the guided decision table cell.

If you specify the list in the "value list", it will automatically create a drop down list and only allow you to choose one value.
If you don't specify anything in the "value list", it take whatever typed in the table cell as a string value.
For example, if you specify ["A", "B", "C", "D"] in the table cell, it take the whole input as one string, you expect to see the source show something
p: lista( element == ["A","B","C","D"] )
but it shows
p: lista( element == "["A","B","C","D"]" )