The description in the Koha Manual for the UnseenRenewals system preference ends with "If you activate this preference, make sure to add a value in the ‘Unseen renewals allowed (count)’ column of the" ... (see it at https://koha-community.org/manual/latest/en/html/circulationpreferences.html#unseenrenewals) It looks like the words "circulation and fines rules" alongside a link to this section of the manual are missing.
Corrected in the manual.