Hi, I am dealing with the same issue as you do. I have Alltrack 2016 BiTdi and I would like to replace the coolant expansion tank for the one without silica bag. When you stand in front of the car, open the bonnet, the silica bag is located on right side inside the coolant expansion tank. The tank has double wall hence why the silica bag is not easy to spot. I know the 2020 BiTdi has coolant tank without silica bag in it (see picture attached) but unfortunately I do not know the part number.
