All InterpolatedCamera in 3D does is lerp the camera's transform. You can do this in 2D yourself with something along these lines:
extends Camera2D
export (NodePath) var target_path
export var speed = 10
var target
func _ready():
if target_path:
target = get_node(target_path)
func _physics_process(delta):
position = lerp(position, target.position, speed * delta)
You can play around with how you move the camera depending on what effect you want. It's really just about moving the camera independent of, but linked to, the target.