I have the 2019 base Zetec model that has Sync3 display, but do not have the sat nav as its not standard on the Zetec, so cannot really help you, though would like to ask a question...
Does the radio music dull down to a lower sound level when the sat nav commands starts talking?
Many cars do that, my brothers SUV does that, rather than kill off the radio sounds entirely during sat nav talk, which can actually sound worse to the ear, as its a more noticeable interruption.
Also if you turn down the radio music does the sat nav voice level remain the same. Hence the sat nav can be heard over the radio easily? (thats another function on my brothers SUV).
Some other Ecosport owner with Sync3 sat nav will hopefully answer this one soon.