I need t plant a good barrier along a fence with fast growing trees, hopefully dense enough to hide a neighbor's yard....
A green tallow berry likely won't grow. A mature seed is white and resembles popcorn. However, the tree is considered invasive, so you might check with an area conservation group about any regulations related to this tree. In the southeastern part of Texas, it has become a problem. I have included links to articles about privacy hedges.
https://extension.okstate.edu/fact-sheets/the-exotic-invasive-chinese-tallow.html
https://texnat.tamu.edu/about/brush-busters/tallowtrees/
https://www.gardeningknowhow.com/ornamental/trees/tgen/evergreen-tree-varieties.htm