Run multiple scenes in Manim

def fade_out(scene: Scene):
    animations = []
    for mobject in scene.mobjects:
        animations.append(FadeOut(mobject))
    scene.play(*animations)


class CombinedScene(Scene):
    def construct(self):
        scenes = [] # TODO: Add scenes here
        for scene in scenes:
            scene.construct(self)
            fade_out(self)

Ref

https://github.com/3b1b/manim/issues/1086