Terminal zsh:killed

This means that something that was added to one of the files like .zshrc is causing trouble.

Temporarily switch to a different shell, like bash, and then tell us what the content of ~/.zshrc is.

You can change the shell to use in Terminal->Settings->General from the default to /bin/bash

This way we can't really see the contents of .zshrc

All these

~

~

are not part of the file, but an artifact of running the less command.

You can try this on the Terminal:

open -a "TextEdit" ~/.zshrc

then copy and paste the contents here using the "additional text" box below.

I don't see how that single command would cause this.

I don't have brew installed on my mac. You could comment out that line, by preceding it with #:

# eval "$(/usr/local/bin/brew shellenv)"

and see if it changes anything.

Also, you may want to check if any of these other files exist, and if so check what is in them:

~/.zshenv
~/.zprofile
~/.zlogin

What is that <feff> before the shell?

The command should just be

sudo chsh -s /bin/zsh

as VikingOSX posted.

It appears your .zshrc is hopelessly corrupted. Did you use something like Homebrew on this Mac?

I don't know what macOS sets for a default, but nothing would be better at this point. Delete it and research how to customize it for what you need.

The shell is still telling you that you have not entirely setup the Zsh shell yet. However, the first thing I would remove would be that homebrew eval statement in your ~/.zshrc file. I have been using the homebrew package manager for several years and at no time has there ever been that eval statement present, which is invoking the shellenv commands that are exploding on you…

Next, I would manually enter the following in the Terminal if it is an Intel MacBook Air:

export PATH=".:/usr/local/bin:${PATH}"



and the following (accounting for the /opt installation locale for homebrew) on an Apple Silicon Mac:

export PATH=".:/usr/local/bin:/opt/homebrew/bin:${PATH}"

Now, finish setting up the default Zsh shell (your admin password will not echo here):

sudo chsh -s /bin/zsh

Then, you create a new ~/.zshrc file with the PATH and PS1 prompts by copy/pasting the following HERE script into the Terminal and then pressing return to run it.

<<"EOF" > ~/.zshrc
export PATH=".:/usr/local/bin:${PATH}"
PS1="%m: %~ %% "
EOF

and once that is done, enter the following command:

source ~/.zshrc

Each time that you launch the Terminal, it will read that ~/.zshrc file.

That Zsh HERE script works fine in a properly functional Zsh shell and should not bork with a zsh: killed error.

Look at your Terminal > Settings panel for your default shell profile. On the Shell tab, it should look like this: