I'm currently reading through and attempting to translate an article about a film in which the phrase "symbolisme appuyé" is used. The full phrase is "et oeuvre au symbolisme appuyé," so I believe it refers to a style of filmmaking that I'm unfamiliar with the French translation of.
Appuyé, used figuratively, means that something is done or expressed with insistence (it can even be slightly negative , meaning it does it too much).
Therefore, une oeuvre au symbolisme appuyé means "a work of art that resorts heavily to symbolism, in a very visible way*.
It is not specific to filmmaking or even to symbolism. You could say for instance:
Il a lancé un regard appuyé.
Il fait souvent des plaisanteries appuyées sur les femmes.
Il a rendu un hommage appuyé à son prédecesseur.