Your system asks for reduced motion, so VFX-JS draws nothing. Demos on this site show plain HTML.

import type { TransitionEffectContext } from "@vfx-js/core";

type TransitionEffectContext = EffectContext & {
    readonly from: EffectRenderTarget;
    readonly holding: boolean;
    readonly progress: TransitionProgress;
    readonly reverse: boolean;
    readonly run: TransitionRun;
    cut(): void;
}