You can typically find the standalone "playable tech demo" on ArtStation or MAWI United's official website.
Sunlight filtering through the canopy (god rays) that updates instantly as you change the time of day. Why It’s "Drool-Worthy"
If you are a developer, Unreal Engine often features "Free for the Month" content where high-end packs like this occasionally appear, or you can download the Megascans trees (which are similar) for free.
Are you looking to the demo to test your PC's performance, or are you interested in using these assets for your own game project?
Released to highlight the power of (real-time global illumination) and Nanite (virtualized geometry), the Broadleaf Forest demo is often cited as a benchmark for photorealism. It features:
Thousands of individual leaves and branches, all reacting to wind and light.
While the full professional asset pack is a paid product for commercial developers, a was released for the public to test their hardware.