Where does the sweat on the concrete slab under vinyl plank flooring come from it has grown mold under the plank and am concerned for obvious health reasons?

Moisture can migrate through a slab foundation. Older slabs did not have a vapor barrier but I have seen it on newer slabs as well. Vinyl flooring will develop mineral deposits or lumps and discoloration. Wood flooring will warp. Carpet will sometimes work without problem or may mildew. Surprisingly, tile works well as it will allow moisture to migrate through the grout joints.