I quickly scanned the nextcloud guides to enable it and it seems this option is not available (or hidden) in the e-cloud settings. As e-cloud is “just” a nextcloud instance, it should be possible to activate this feature, but for that we propably need to contact support as in the guides it is spoken of a setting inside an admin account. As for now e-cloud is secured by HTTPS and server side encryption which we need to trust.
But this is a neat feature I didn’t know until now. I’d definitly want that too.