Giant Defy 2018 front brake cable routing problem
I did a quick google image search on 'Giant Defy 2018', found a couple of pics from the left hand side of the bike.

The front brake cable is supposed to run outside then down the back of the left fork leg.

As you are assembling this yourself I guess you did not purchase at a bike store. If you did though, take it back and have them fix the issue and check for other problems.