I wanted to suggest this idea but found it was suggested already six years ago but for some reason, this simple but important feature has not yet been implemented.
So I’m quoting the original request someone sent in 2018:

Very often Waze starts up navigation facing the wrong driving direction. The direction is rectified as the vehicle starts moving, but it can be too late for the initial turn.

Please add the ability to switch driving direction when navigation starts, via a button.