So, a way around this is:
- Set the tab with the unselected default icon image that you want to use in the "BAR ITEM" section of the Attributes Inspector:

- Click on the Identity Inspector and in the DEFINED USER ATTRIBUTES section, click the + button to add a new value.
KEYPATH: selectedImage (IT SHOULD BE IT !!!)
TYPE: Image
VALUE: the name of the selected / highlighted icon image. I use Images.xcassets for my image objects.

Launch the app. You will notice that the image changes to the selected (and not just the highlighted version).
It works like a charm.
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