"Apple replaces shell designed 30 years ago with one designed 29 years ago"
FISH, the "Friendly Interactive Shell"-- now 15 years old-- provides a more substantial leap forward in autocompletion and auto-suggestion, while adding some breaking changes to improve the overall design of the language and user experience. It's still highly compatible with bash or zsh syntax for day-to-day usage.
Try `fish_config` to launch a browser where you can select a theme. Enjoy autocompletion for 500 commands by default. Need help for a built-in command? Try `help test` to read the docs for the `test` command in your browser.