Q.How Do I Propagate Swiss Chard Which Has Trailed And Has Multiple Shoots/new Plants?
The long stem in the middle (from when the plant bolted this summer) has stems growing new, nice-looking shoots, but they don’t have their own root systems yet. Can I divide these and replant? Will they grow roots?

Certified GKH Gardening Expert
No, the plant will be far too old to grow a root system. After harvest, the plant will begin to die off. Taking a tip cutting will fail. It is best to start over from seed each season, or every few weeks for multiple harvests.
https://www.gardeningknowhow.com/edible/vegetables/swiss-chard/how-to-grow-swiss-chard.htm