Chinese characters made in Japan are called wasei kanji (和製漢字 “Japanese-made Chinese characters”) or kokuji (国字 “national characters”) in Japan. There are a few hundred in existence, but not many are commonly used. The most common ones are found in the verbs 働く (hataraku, to work), 込む (komu, to be crowded / to go into), 匂う (niou, to smell). Chinese already has its own words for these concepts, so these kanji have not been borrowed back into Chinese. However, Chinese readings of these characters do exist, based on their phonetic components: dòng, yū, and xiōng respectively.
Other wasei kanji include names of fish like 鰯 (iwashi, sardine) and trees like 樫 (kashi, evergreen oak), which go by different names in Chinese. Again, Chinese readings of these characters exist despite not being used in the Chinese language: ruò and jiān respectively.
Some wasei kanji like 畑 (hatake, field of crops) are used in Japanese names. In this case, the kanji is used in Chinese when referring to a Japanese person’s name. It is read as tián in Chinese.
The only wasei kanji that I am aware is used in Chinese vocabulary is 腺 (sen, gland), read as xiàn in Chinese. This is a newer character, created by the Japanese scholar Udagawa Genshin in the late 1700s or early 1800s, and later borrowed “back” into Chinese.
Note: wasei kanji (Chinese characters made in Japan) are distinct from wasei kango (Chinese words made in Japan from existing Chinese characters). The latter are much more common, especially in the sciences, and they make up a lot of modern Chinese vocabulary. For example, 経済 (economy), 哲学 (philosophy), 心理学 (psychology), 宗教 (religion), 物理 (physics), 数学 (mathematics), 国際 (international), 資本 (capital), 社会 (society), and a LOT more. It’s really surprising to see how many modern Chinese words derive from Japanese.