This morning, my Mac OS terminal told me to switch to zsh. Here's how it went.

This is what appeared when opening a terminal window:

The default interactive shell is now zsh.
To update your account to use zsh, please run `chsh -s /bin/zsh`.
For more details, please visit https://support.apple.com/kb/HT208050.

So I did, and upon opening a new terminal window, my PATH had been reset. Running flutter wouldn't work anymore. A quick search reveals that while in bash, the settings file is ~/.bash_profile, for zsh, it is ~/.zshrc. I copy pasted the line that added flutter to the $PATH and it worked.

export PATH=$HOME/flutter/bin:$PATH

What's the difference between bash and zsh? I'll look it up some other day.