GSX surely recognizes the STANDARD Parking Brake, that is the standard variable that controls the Parking Brakes. 3rd party airplane might not use the standard system, and have custom variables on their own, so they need to configured before they can be used by GSX.
While in previous versions, it wasn't possible for users to change this, and in order to have a plane using a custom Parking Brake being recognized you had to wait for a GSX upgrade, with the November 15th update, there's no need to wait us to add support for custom Parking Brake systems.
https://www.fsdreamteam.com/couatl_liveupdate_notes.htmlGSX (all versions) NEW: Added Parking Brakes Test XML expression in the Airplane Configuration editor, to allow adding support for airplanes with non-standard Parking Brake systems and Chocks to be user-editable without waiting to be supported by GSX internally.
The option is explained in detail in the manual, at Page 62, with some examples. Of course, we cannot possibly know every custom string of every airplane out there so, in case of ProSim, I think your best bet would be asking their support for the name of the custom variable they must have used for their custom Parking Brake system, so you can use it in the airplane configuration editor as part of a custom XML expression, following the examples in the manual.