MacOS 13.3.1, Adobe Illustrator 27.4.1
Also reported on Windows same version of Illustrator.

Steps to reproduce.
To see problem, run this script
```
(function () {

var doc = app.documents.add();

var tf1 = doc.textFrames.add();
tf1.position = [100, 100];
tf1.contents = 'Break\u000Ame.';
alert('Linefeed (10)\n charCode = ' + tf1.contents.charCodeAt(5));

var tf2 = doc.textFrames.add();
tf2.position = [200, 100];
tf2.contents = 'Break\u0003me.';
alert('End-of-text (3)\n charCode = ' + tf2.contents.charCodeAt(5));

})();
```
I would expect the text on the left to have a line feed (u+000A) character, but it is converted to a carriage return (u+000D).
The text on the right is a workaround, using an unexpected character (u+0003).

There is a discussion here.

This silent conversion is unexpected, and never wanted by the user (the scripter).