I am still in the operational phase of the system
my problem is that my system has basic functions but it will have functions that will be added according to an environment and specific constraints (so it will have a behavior and constraints to manage according to each configuration)
and I don’t know how to do that
It sounds to me that your issue is not really variant architecture management at all. You need to define an architecture that can be functionally compliant when deployed in different environments. As the solution architect you can determine the most optimal solution in this regard. Either try to define a super architecture that address all the constraints of the operational environment or include different logical components that exist to address the constraints in each of the environments. This will more than likely lead to different physical components and of course a product breakdown structure that can create a compliant solution depending on how it is instantiated from the bill of material, i.e. built and configured for a particular deployment.