zsh can't see and doesn't load the ~/.zshrc startup file After upgrading to Catalina and encountering the zsh upgrade reminder when launching Terminal, I've decided to switch to zsh.
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.

However, I'm having trouble getting Terminal/zsh to recognize the .zshrc startup file located in my home folder. ~/zshrc isn't loaded on launch, and executing source ~/.zshrc returns source: no such file or directory.
The file only contains one line, an alias tying python to python3.
The issue turned out to be that .zshrc had a hidden .txt file extension. Somehow it was automatically named .zshrc.txt, probably when I used TextEdit to edit it, and source doesn't infer the text extension. Finder also doesn't display the .txt extension by default unless you inspect the file, so I hadn't noticed the issue.