In the new UE5.5 engine, FleshAsset did not find the Generate Tetrahedral Collection node
I ran into this but found the answer, it seems they split that into two separate functions, potentially for readability. To get this functionality back just send your mesh into a StaticMeshToCollection (or SkeletalMeshToCollection) and then feed the collection result into CreateTetrahedron on the Source collection. After that it should function the same as the old GenerateTetrahedralCollection Node. Hope this helps ^v^.
Edit: Just realized that the video posted above me shows this in a youtube video, probably should have looked at that closer before posting.

