Nextcloud iOS before 3.4.2 suffers from an information disclosure vulnerability when searches for sharees utilize the lookup server by default instead of only on the local Nextcloud server unless a global search has been explicitly chosen by the user.
https://hackerone.com/reports/1167919
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-m7w4-cvjr-76mh