У вашего броузера проблема в совместимости с HTML5
Nextcloud End-to-end Encryption is designed to offer the ultimate protection for your data, even in case of a compromised server. This talk aims to explain its design and purpose to a technical audience.
Learn more on https://nextcloud.com/endtoend
Recording from the 34th Chaos Communication Congress
(34c3) Stage Chaoswest, https://media.ccc.de/v/34c3-ChaosWest-12-nextcloud_end_to_end_encryption