WeChat is designed with privacy and safety in mind. To ensure that only you and your intended recipient(s) can view your messages, WeChat does not store chat data on its servers.
However, your chat data will remain available within the app on your device as long as the app is not removed and your phone has sufficient storage space.
If you want to back up or transfer your chat history to a new device, you can use the Migrate Chats to Another Device or Favorites feature.