When clicking on the "Reference qual condition" filter on the "Lookup select box" variable, there is an error message

The field "Reference qual condition" is not intended to be used with the "Lookup select box" type variable.

The field "Reference qual condition" is not intended to be used with the "Lookup select box" type variable.

 

Instead, we could use the "Reference qual" field, where we can specify the reference qualifier.

 

Please refer to the section "Advanced reference qualifier" in this documentation,

 

Also, these community articles could also be used as a reference,