Show on a table selected values that appear only once even when more values are selected on filter

[lailarhc]

Hello.
I'm sorry if the title is confusing. I'll try to explain better.
I have a  chart table that only lists employees (Servidor) that have not taken any courses (Curso) if said employee is selected on the filter.

Like so:

I need that chart table to keep on showing only employees who have not taken any courses even if more employees are selected. But whenever that happens, according to the calculation condition I set, nothing shows on the table.

Like so:

It should still display the employee from the image before this one, listing him as the only employee selected that does not have any courses. If an employee appears only once, that means he does not have any courses.

Here's my table's expression, where Servidor represents the employee's dimension:
=Aggr(Only({$ <Servidor = {"= Count(Servidor) = 1"}>} Servidor), Servidor)

Here's what I've put on the Calculation Condition in the data handling section (honestly, I've just copy and pasted the table expression):

GetFieldSelections(Servidor) = Aggr(Only({$ <Servidor = {"= Count(Curso) = 1"}>} Servidor), Servidor)

How can I achive what I want?
Thank you in advance