Another project from several years ago.
The kitchen island in our new house is large - about 4 x 12 ft. The overhanging part of the countertop was not correctly supported. Specs say that an overhang greater than 14" must be supported; this is 21." The industry spec says it must be supported at least 12" from the mounting surface. The corbels installed by the builder were decorative only and protruded about only 6" - actually crap that supported nothing. The countertop seemed to droop about 1/16 - 1/8" across the 21" - splashed water ran across and off the edge. Something had to be done, but the solutions from the builder (Patrick Malloy Homes) were a joke.
After looking extensively, it became evident that wood corbels could not be fastened solidly enough to support that weight. I finally found steel supports that are 1/2" thick, 2" wide and extend 12" - the rated load is 125 pounds each. Made the builder install them, removing drywall down to the studs.
To cover the really ugly steel brackets, I designed and made corbels of poplar 4" thick with 14" protrusion. Then routed the back to accommodate and hide the steel. The result turned out nicely.
These are the brackets I used: https://ironsupports.com/products/standard-front-mount-countertop-l-bracket?ref=yotpo_106&variant=15840870498375