A heavy yoke is a metaphor for very difficult labor and cruel treatment. This metaphor is continued in verses 10 and 11. See how you translated a similar phrase in [2 Chronicles 10:04](./03.md). AT: "treated them cruelly" or "forced them to work very hard" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This metaphor means that Rehoboam is more cruel and intimidating than his father. AT: "I rule much more harshly than my father ever did" or "I am much harsher than my father" (See: [[rc://en/ta/man/translate/figs-metaphor]])