Yes, the traffic jam assist is only with DSG, but that is obvious from the construction side of things, as with manual shift gears one cannot start moving from zero speed automatically. The adaptive cruise control functions similarly, until you have to change the gears manually.
But with rear traffic alert, there is nothing that requires the DSG in order for it to work (as evidenced that it was available in MY2016 (and maybe others as well). That’s why it seems to me that it must be part of the VW cost cutting exercises to remove it from manual in MY2018.
Therefore, I assume there should be a way to enable it with VCDS and some of you VCDS wizards might have found out how.
(Similarly, my MY2016 did not have Traffic Sign Recognition enabled from the factory, but with the lane departure camera already on the car, it was simple to enable it through VCDS. That’s why I assume this must be a similar case.) Any help from the VCDS wizards out there?