Can I use PHP inside XThreads settings?

[Jazzy]

Hi Team,
I have a question regarding this option.

So, I want to create a listbox as Custom Thread Field. The Values for this listbox should be the topics the respective user wrote in forum A. With creating a new topic or with each new reply in forum B, the users should be able to choose from this listbox. After submitting the newthread/newreply,  I want to add the result of this selection to the postbit.

Both plugins, (xThread-Custom Thread Fields and PHP in Templates) are active.

At the moment my settings look like this (pls see Attachement). I entered the query to call all topics in fid32 (= forum A) that the logged in user wrote and put it in the values list.

However when I create a new topic in Forum B (where I activatated this custom thread field) I receive the blank code on newthread.

Did I understand above question wrong, or did I make a mistake?
Can I only post existing mybb-variables but not whole and own queries?