See the standard:
Finally, BACKSLASH characters in values MUST be escaped with a BACKSLASH character. NEWLINE (U+000A) characters in values MUST be encoded by two characters: a BACKSLASH followed by either an ‘n’(U+006E) or an ‘N’ (U+004E).
Here is an example file produced by Delta Chat that does not render correctly because of this, observe the multi-line NOTE property:
BEGIN:VCARD
VERSION:4.0
EMAIL:pixsocial@arcanechat.me
FN:PixelSocial
KEY:data:application/pgp-keys;base64\,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
PHOTO:data:image/jpeg;base64\,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
NOTE:I am a bot that allows you to interact in PixelSocial social network.
Source code: https://github.com/deltachat-bot/pixelsocial
REV:20260224T094739Z
END:VCARD