降版本沒用，換「Ubuntu軟體」內其他版本無用，最後用戶端改用owncloud Desktop Client解決！
You can add the repository key to apt. Keep in mind that the owner of the key may distribute updates, packages and repositories that your system will trust (more information). Run the following shell commands as root to trust the repository:
wget -nv https://download.owncloud.org/download/repositories/production/Ubuntu_18.04/Release.key -O Release.key apt-key add - < Release.key
Run the following shell commands as root to add the repository and install from there.
echo 'deb http://download.owncloud.org/download/repositories/production/Ubuntu_18.04/ /' > /etc/apt/sources.list.d/owncloud.list apt-get update apt-get install owncloud-files