Why is the magnitude of mutual flux in a transformer independent of the current in primary?
Mutual coupling is dependent on the core material only that is shared between
windings.but it does require an excitation voltage and current to energize this magnetic coupling. But that is independent of load current.
Inductance is the ability to store charges by the change in magnetic orientation. When they have reach the limit of alignment they can no longer move , store energy and inductance drops rapidly while harmonic content rises at the same rate and eventually the wire behaves just the low wire resistance at peak voltages