Do I need to quarantine when going to Banna from Nanchong?

No need

As of October 5, Xishuangbanna is currently a low-risk area, but the Dehong epidemic has occurred frequently recently. Travel to Xishuangbanna from medium- and high-risk areas needs to follow the Xishuangbanna isolation/nucleic acid policy. People who have a history of living in Tibet, Guizhou, and Xinjiang and enter (return to) Xishuangbanna Prefecture will be subject to 7-day centralized quarantine. Five nucleic acid tests must be completed during the quarantine period (days 1, 2, 3, 5, and 7), and the centralized quarantine medical observation period shall be calculated from the date of departure from Tibet, Guizhou, and Xinjiang. Those who have entered (or returned to) Xishuangbanna Prefecture for more than 7 days must complete at least "3 days and 2 inspections"; if the stay is less than 7 days, the gap in centralized isolation time shall be made up according to the principle of filling up the gap.