Nexcloud desktop is the Desktop sync client for Nextcloud. An attacker can inject arbitrary HyperText Markup Language into the Desktop Client application in the notifications. It is recommended that the Nextcloud Desktop client is upgraded to 3.6.1. There are no known workarounds for this issue.
https://hackerone.com/reports/1668028
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-c3xh-q694-6rc5