Yandex support refers to Duplicati not working correctly)
Yandex stopped working with Duplicati using the built-in webdav protocol in 2020, because many realized why not store backups in a cheap cloud? The cost of Yandex Disk is $ 15 per year for 1 TB.
Moreover, Yandex has Yandex.Cloud, which is much more expensive and which involves the use of Duplicati Backup to Yandex Object Storage via Duplicati | Yandex Cloud - Documentation