Boris Nextcloud on Qnap from Android or ios definitely dont work. Neither for Nextcloud or Webdav connections from BC. In both cases you throw the self-signed certificate complaint even though it is a LetsEncrypt certificate issued via the QTS automation.
It is notable that BC is the only app on either Android or IOS that fails on wither native nextcloud or webdav connections.
It is also notable that despite several tries with BC support that the best answer has been: ‘your server is configured wrong’ absent any detail as to how it would have to be configured for BC to work against it.
It is both notable and disappointing that the forums show this to be an issue stretching back years without a solution offered.