Is “Is there currently no record of Duke Xuan of Chen, the ruler of the state of Chen, in historical sources, and is he only depicted in novels as killing Prince Yukou and participating in the campaign against Chu?” true?

The candidate document's claim of 'no record in historical sources' is wrong -- and that phrase is the candidate list's own assertion, not a quotation from any classical text. The 'Records of the Grand Historian, Hereditary House of Chen and Qi' clearly records the life and reign of Duke Xuan of Chen (Chujiu): 'Duke Xuan later had a favoured concubine who bore a son named Kuan; wishing to establish him, he killed his heir apparent Yukou. Yukou had always been close to Wan, son of Duke Li, and Wan, fearing disaster would reach him, fled to Qi.' The 'Hereditary House of Tian Jingzhong Wan' likewise records: 'In the twenty-first year of Duke Xuan, he killed his heir apparent Yukou.' The episodes in novels such as 'Chronicles of the Eastern Zhou Kingdoms' therefore rest on solid historical ground. (Correction: the one who fled to Qi was Chen Wan, son of Duke Li, not Duke Huan.)