The limit is defined by the number of characters, not the number of entries. A multi-text attribute in Openprise can have a maximum of about 8100 total characters.
The actual maximum is defined in bytes (32766 max), so if you consider a character typically takes 4 bytes (UTF-8 type for example), the maximum is 8191 characters. Note that a character includes any punctuation, non-printable character, or space.