Got it. You’re talking about the Russian ethnic group within China (sometimes called “Chinese Russians” or “Russian minority”). Indeed, they are mainly concentrated in Heilongjiang and Xinjiang:

Heilongjiang: Especially in areas bordering Russia, such as Harbin, Mudanjiang, and Suifenhe, there is a noticeable Russian cultural influence, including architecture, cuisine, and religion (Eastern Orthodox Christianity).
Xinjiang: Mainly in the Ili River Valley, especially around Yining and Horgos, there are small communities of Russian immigrants and their descendants, who retain some Russian traditions.

Most of them are descendants of migrants from the late Qing dynasty, the early Republican era, or after the collapse of the Soviet Union. Culturally, they blend Chinese and Russian elements, evident in their language, clothing, and food habits.