The issue isn’t direction but rather having multiple branches as a river only includes channel(s) going downstream from a single point. Without that definition a river’s length would be the length of every river connected to it.
Thus the Mississippi and Ohio river are considered different rivers even though their waters mix and both flow downstream through the same channel.
According to this definition then Iraq’s man-made river (Saddam’s river) is longer at 565 km. the official role of the river was to collect irrigation water from Mesopotamia fertile land all the way to the Persian Gulf, though the real reason Saddam built it was to dry the Arab Marshes as it was difficult to contain the rebels in the marshes. https://ar.wikipedia.org/wiki/%D8%A7%D9%84%D9%85%D8%B5%D8%A8...
You do have a point though that this new river in Egypt may be the 'largest' on some other metric.