On a fresh bare metal installation of Debian 9.4 stretch, with no GUI,
I installed owncloud-client-cmd.

root@dzur:/etc# pre owncloud
libowncloudsync0	2.2.4+dfsg-2		amd64
owncloud-client-cmd	2.2.4+dfsg-2		amd64
owncloud-client-l10n	2.2.4+dfsg-2		all
root@dzur:/etc#


I then executed the following:

charles@dzur:~$ /usr/bin/owncloudcmd --user charles --password <obfucated> /home/charles/nextcloud https://nextcloud/nextcloud
QIODevice::read (QFile, "/home/charles/.local/share/data//ownCloud//cookies.db"): device not open
Set proxy configuration to use system configuration
Cannot load system exclude list or list supplied via --exclude
Aborted
charles@dzur:~$

I solved that by going to a backup from a prior installation
(/crc/dzur), and copying in the relevant files:

charles@dzur:~$ mkdir -p /home/charles/.local/share/data//ownCloud/
charles@dzur:~$ /usr/bin/owncloudcmd --user charles --password <obfuscated> /home/charles/nextcloud https://nextcloud/nextcloud
QIODevice::read (QFile, "/home/charles/.local/share/data//ownCloud//cookies.db"): device not open
Set proxy configuration to use system configuration
Cannot load system exclude list or list supplied via --exclude
Aborted
charles@dzur:~$ ls /crc/dzur/home/charles/.l
.lesshst  .local/
charles@dzur:~$ ls /crc/dzur/home/charles/.local/share/
applications/       keyrings/           shotwell/           xfce4/
data/               orage/              shotwell.old/       xorg/
gnome-sudoku/       recently-used.xbel  Trash/
gvfs-metadata/      ristretto/          vlc/
charles@dzur:~$ ls /crc/dzur/home/charles/.local/share/data/ownCloud/
cookies1.db  cookies.db  folders  owncloud.cfg
charles@dzur:~$ ls /crc/dzur/home/charles/.local/share/data/ownCloud/* ~/.local/share/data/ownCloud//crc/dzur/home/charles/.local/share/data/ownCloud/cookies1.db
/crc/dzur/home/charles/.local/share/data/ownCloud/cookies.db
/crc/dzur/home/charles/.local/share/data/ownCloud/owncloud.cfg

/crc/dzur/home/charles/.local/share/data/ownCloud/folders:
ownCloud

/home/charles/.local/share/data/ownCloud/:
charles@dzur:~$ cp -rp /crc/dzur/home/charles/.local/share/data/ownCloud/* ~/.local/share/data/ownCloud/
charles@dzur:~$

Once more, with feeling:

charles@dzur:~$ /usr/bin/owncloudcmd --user charles --password <obfuscated> /home/charles/nextcloud https://nextcloud/nextcloud
Set proxy configuration to use NO proxy
Cannot load system exclude list or list supplied via --exclude
Aborted
charles@dzur:~$

Some googling produced https://github.com/owncloud/client/issues/4955
That lead me to solve that problem by again copying in from a backup:

root@dzur:/etc# cp -rp /crc/dzur/etc/owncloud-client/ .
root@dzur:/etc# ll owncloud-client/
total 20
drwxr-xr-x   2 root root  4096 Apr  6 12:53 ./
drwxr-xr-x 105 root root 12288 May 28 08:34 ../
-rw-r--r--   1 root root   362 Sep 27  2016 sync-exclude.lst
root@dzur:/etc#

The next test produced a sucessful run.

On a headerless system, a GUI is superfluous. A command line only
program should not depend on GUI versions of the program. So the
owncloud-client-cmd package should (if necessary) install a minimal
etc/owncloud-client/.

The lack of the user's ~/.local is probably something that should be
solved on the first run of the program, so I suggest that is an
upstream bug.

Dear submitter,

as the package owncloud-client has just been removed from the Debian archive
unstable we hereby close the associated bug reports.  We are sorry
that we couldn't deal with your issue properly.

For details on the removal, please see https://bugs.debian.org/969422

The version of this package that was in Debian prior to this removal
can still be found using http://snapshot.debian.org/.

Please note that the changes have been done on the master archive and
will not propagate to any mirrors until the next dinstall run at the
earliest.

This message was generated automatically; if you believe that there is
a problem with it please contact the archive administrators by mailing
ftpmaster@ftp-master.debian.org.

Debian distribution maintenance software
pp.
Sean Whitton (the ftpmaster behind the curtain)

...

Please test the new version of owncloud-client available in Debian
experimental and reply to the bug whether this issue is fixed yet.

Really?

After adding experimental to a stable (Bullseye) system, I ran:

--------------------------------------------------
root@amanda:~# apt-get -t experimental install owncloud-client-cmd
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  libdouble-conversion3 libmd4c0 libowncloudsync0 libqt5core5a
  libqt5dbus5 libqt5gui5 libqt5keychain1 libqt5network5 libqt5sql5
  libqt5sql5-sqlite libqt5svg5 libqt5widgets5 libxcb-icccm4
  libxcb-image0 libxcb-keysyms1 libxcb-render-util0 libxcb-xinerama0
  libxcb-xinput0 libxcb-xkb1 libxkbcommon-x11-0 libxkbcommon0
  owncloud-client-l10n qt5-gtk-platformtheme qttranslations5-l10n
Suggested packages:
  qt5-image-formats-plugins qtwayland5

...

--------------------------------------------------

Even if the code is fine, the list of dependencies is unacceptable.

After installing anyway, I ran:

--------------------------------------------------
charles@amanda:~$ /usr/bin/owncloudcmd --user charles --password <obfuscated> /home/charles/nextcloud https://nextcloud.localdomain/nextcloud
10-19 13:05:38:749 [ info sync.accessmanager ]:	2 "" "https://nextcloud.localdomain/nextcloud/ocs/v1.php/cloud/capabilities?format=json" has X-Request-ID "76ed3f60-4492-4794-acd3-ac18e7e5aa19"
10-19 13:05:38:749 [ info sync.networkjob ]:	OCC::JsonApiJob created for "https://nextcloud.localdomain/nextcloud" + "ocs/v1.php/cloud/capabilities" ""

<much cruft omitted.>

10-19 13:05:41:679 [ fatal default ]:	Cannot load system exclude list or list supplied via --exclude
Aborted
charles@amanda:~$
--------------------------------------------------

So I copied in an old copy of ~/.local/share/data/ownCloud. Then ran the same command line again.

--------------------------------------------------
charles@amanda:~$ /usr/bin/owncloudcmd --user charles --password <obfuscated> /home/charles/nextcloud https://nextcloud.localdomain/nextcloud
10-19 13:20:32:638 [ info sync.accessmanager ]:	2 "" "https://nextcloud.localdomain/nextcloud/ocs/v1.php/cloud/capabilities?format=json" has X-Request-ID "5a051192-0f74-40e6-accc-f065b233bd00"
10-19 13:20:32:639 [ info sync.networkjob ]:	OCC::JsonApiJob created for "https://nextcloud.localdomain/nextcloud" + "ocs/v1.php/cloud/capabilities" ""
10-19 13:20:32:641 [ warning sync.networkjob ]:	QNetworkReply::ConnectionRefusedError "Connection refused" QVariant(Invalid)
10-19 13:20:32:641 [ info sync.networkjob.jsonapi ]:	JsonApiJob of QUrl("https://nextcloud.localdomain/nextcloud/ocs/v1.php/cloud/capabilities?format=json") FINISHED WITH STATUS "ConnectionRefusedError Connection refused"
10-19 13:20:32:641 [ warning sync.networkjob.jsonapi ]:	Network error:  "ocs/v1.php/cloud/capabilities" "Connection refused" QVariant(Invalid)
10-19 13:20:32:641 [ debug default ]	[ main(int, char**)::<lambda ]:	Server capabilities QJsonObject()
Error connecting to server
charles@amanda:~$
--------------------------------------------------

This is running against a server Nextcloud 22.2.0. So it is possible
that divergence between the server and client have made it impossible
for me to test.

owncloud-client was removed from Debian and then reintroduced back into
Debian, I was just doing reopening and triage of the bugs closed by the
removal of the package from Debian.
...

That is to be expected when mixing packages from different suites,
if it reaches backports then the deps should be more appropriate.

I see, thanks for trying anyway.