Without signing in to a Google Account, Chromium does pretty well in terms of security and privacy. However, Chromium still has some dependency on Google web services and binaries. In addition, Google designed Chromium to be easy and intuitive for users, which means they compromise on transparency and control of internal operations.
ungoogled-chromium addresses these issues in the following ways:
These features are implemented as configuration flags, patches, and custom scripts
These are the core features introduced by ungoogled-chromium
These are the non-essential features introduced by ungoogled-chromium.