Do forests with Vietnamese districts on them count as "unimproved features"?
In Civ 6, governor Reyna can give +2 gold for each unimporved feature in a city. Do forests with Vietnamese districts on them count?
No. Unimproved means not touched.
Anything you build on a tile (with a builder) is called an improvement, regardless of whether it partially preserves some of the scenery or not.