Apparently Cloud Firestore console does not display newline characters inside strings. Is there a way to inspect them?
This string
Strings are stored unmodified, but various parts of the Firestore console show the newline character in different ways. Also see my previous answer on Firebase Firestore new line command and Doug's answer here: New Line Command (\n) Not Working With Firebase Firestore Database Strings.
Since the behavior is confusing to you, please file a bug report. But rest assured: your newline characters are stored and read correctly.