To create a line-probe, right-click the Derived Parts node and select New Part > Line-Probe...
Typically, an in-place dialog would be used for this process, and it would appear as soon as you execute this pop-up menu action.
However, if the conditions for activating this dialog are not met, then this action causes the new line-probe to be added to the simulation tree immediately, and you can define the part using the properties.