The Dragon Republic by R.F. Kuang (2019) Harper Voyager

Rin, the heroine of the Poppy Wars, returns, addicted to heroin in an effort to quiet the murderous Phoenix inside her mind and to escape the guilt of how she ended the war.  This time, the Dragon warlord seeks to overthrow the empress and establish a republic with the help of foreigners who have advanced technology, but will not provide help until they see that the Dragon lord's plan will work.  Only the empress is not so easy to defeat, and the Dragon lord is not really helping a republic form.  In the end, he will do whatever he needs to preserve his family's position and safety.