If you know how triplanar mapping works, then the mapping to unreal shader graph isn’t particularly hard – you have world position as an available input, and you’ll map various projections of the XYZ into UV into the texture coordinates you use, and then use a couple of if() nodes to select which coordinate set to use, and then six texture fetches (four, if you really optimize) for each material component (diffuse, normal, etc.) that in turn get lerped into the output.
It’s just quite tedious – a lot of copy-paste!
There’s a free “Landscape Material Pro v2” on the Marketplace right now. If you go to the support page for that product, and follow to the video tutorials, there’s one video tutorial on how to copy-paste a bunch of things around to make that material use tri-planar mapping. You might get something out of following along there.