But if we checked the Embedded stairs in a/c GSX cfg it doesn't suppose to prevent the spawn the GSX stairs? this is how it works on P3D Ver anyway an other option will be nice that will prevent the spawn
No, it never worked like that in P3D, nothing has changed, if the airstair has a condition ( the XML expression ), it means it's optional, it's only used depending on that condition, so you can choose to use it or not. But without a question before selecting a gate, the real choice is only on Departure, provided you extended the stairs before you open the GSX at the gate.
If there's no condition, it means it will always be used, that's the case with planes like the CRJ, where the embedded stairs have no condition, means they will always be used.