Hmm I guess you have already tried this, but this just works on my project.
In this case it the scale and the transparency at the same time.
func pickup() -> void:
$Tween.start()
func _ready() -> void:
$Tween.interpolate_property($AnimatedSprite, "scale"
, $AnimatedSprite.scale, $AnimatedSprite.scale * 3, 0.3
, Tween.TRANS_QUAD, Tween.EASE_IN_OUT)
$Tween.interpolate_property($AnimatedSprite, "modulate"
, Color(1, 1, 1, 1), Color(1, 1, 1, 0), 0.3
, Tween.TRANS_QUAD, Tween.EASE_IN_OUT)