I think that may be an unintended type restriction on that card. Good catch.
In the meantime, you should be able to solve this issue by taking the values list and putting it into an Assign card. Once you’ve put that input in, go to the output copy of it below and change the type so that it’s not a List anymore as shown in the screenshot below.
Then, just use that String output in the Smartsheet card. It should accept that type with no problem.