What the style is actually made of
Strip the nostalgia away and this look is three concrete things: hand-painted texture that keeps brush direction visible, foliage rendered in distinct layers rather than as a mass, and warm light scattering through atmosphere. Those are the elements the template reproduces, and knowing them is useful — it tells you what to feed it.
Choosing a source
Give it depth and green. A garden, a tree-lined street, a hillside, a window looking out onto either. Flat interiors and close-up subjects have no foliage to layer and no atmosphere to scatter light through, so the result reads as a colour grade rather than a painting. If your scene has a strong foreground, middle distance and sky, the conversion has all three of its ingredients.