Landscape Material Coverage

Hi,it’s me Fiorenzone. I made a very simple landscape material and right now I’m trying to apply it to the landscape but I don’t know which is the best way to do it. I’ve already seen all the tutorial and docs pages that I could find but the results are unsatisfying and it seems that nobody knows how to accomplish something similar to this: (sorry for the link but Idk why I can’t upload the pic directly).

It is from a quixel video on YT ( and even if at some point in the video is possible to see the material I still can’t understand the best workflow to obtain something like that. He says that he used a mask exported from WM but that’s the only thing I know about so I hope that some of you can tell me more how to make a good splatmap to obtain a result like that one