Planet 9 may or may not exist. We do not know. The following article explains this possibility of our solar system.
https://www.msn.com/en-us/news/technology/could-planet-nine-be-lurking-in-the-outer-solar-system-astronomers-intensify-search-for-the-elusive-giant/ar-AA1qdp0i?ocid=msedgdhp&pc=DCTS&cvid=81f7d379415a4dc1a2eca60444f60f06&ei=31