nextcloud-desktop/doc/options.rst

You have the option of starting your Nextcloud desktop client with the 
``nextcloud`` command. The following options are supported:

``nextcloud -h`` or ``nextcloud --help``
        Displays all command options.

The other options are:

``--logwindow``
        Opens a window displaying log output.

``--logfile`` `<filename>`
        Write log output to the file specified. To write to stdout, specify `-` 
        as the filename.

``--logdir`` `<name>`
        Writes each synchronization log output in a new file in the specified 
        directory.
        
``--logexpire`` `<hours>`
        Removes logs older than the value specified (in hours). This command is 
        used with ``--logdir``.

``--logflush``
        Clears (flushes) the log file after each write action.

``--logdebug``
        Also output debug-level messages in the log (equivalent to setting the env var QT_LOGGING_RULES="qt.*=true;*.debug=true").
)

``--confdir`` `<dirname>`
        Uses the specified configuration directory.