As Ghislain Girardot notes, this isn't exactly a tutorial, but rather a narrated devlog video and a technical breakdown covering the artist's previous foliage interaction systems and explaining his most recent custom strand-based simulation using Blueprints and Niagara.
In the past, the artist has experimented with Vertex Shader, Blueprints, Render Targets, and more. If you're interested in technical art and want to explore previous interactive foliage tests in detail, check out these Ghislain Girardot's breakdowns: