I first hit the lack of LF line endings support at around age 11 on Windows 98. It’s genuinely pretty weird to realize it’s finally fixed
It's slightly annoying that you have to twiddle a bunch of the preferences to make it a workable plaintext editor. Apple should just delete its rich text functionality, now that they bundle a real word processor (Pages) with the OS.
In TextEdit -> Preferences..., select the "Plain text" radio button. New documents are created as plain text now.
New Document:
Format:
Plain Text (select)
Options:
Check spelling as you type (disable)
Correct spelling automatically (disable)
Smart copy/paste (disable)
Smart quotes (disable)
Smart dashes (disable)
Text replacement (disable)
Open and Save:
When Opening a File:
Display HTML files as HTML code instead of formatted text (enable)
Display RTF files as RTF code instead of formatted text (enable)
When Saving a File:
Add ".txt" extension to plain text files (disable)
Plain Text File Encoding:
Opening files = Unicode (UTF-8)
Saving files = Unicode (UTF-8)