I'm in Bishop's Stortford, hence a bit of local knowledge, especially on routing to/from Harwich for the ferry.
Your original Komoot route would have been quite unpleasant in parts. The Braintree to Colchester road in particular is a fast A road, quite narrow, and quite busy during the day.
On the RWGPS route, I stopped the route just short of the terminal. Where the route stops there's a footpath on the right you can go onto, so effectively you go in a straight line rather than going round the left bend. You can then cut through to the ferry entrance on the right across the car park. EDIT: I've just updated the route to show what I mean.
Enjoy your ride in the Netherlands.