Known. A clay dragon and a clay phoenix were found in the same grave.
The grave is at the Zhaizita Stone City site, in Jungar Banner, Ordos City, in Inner Mongolia. It is about 4,300 years old, around 2300 BC, in the Yongxingdian culture of the Longshan period. A jade disc set with turquoise was in the grave too. It is the earliest clear dragon-and-phoenix pair yet found in northern China.
The page does not say what is still argued.
https://www.ancient-origins.net/news-history-archaeology/earliest-dragon-phoenix-pairing-00103118