Sorry, the Alpine one wouldn't be helpful anyway. The Arch package (https://www.archlinux.org/packages/community/x86_64/nextcloud-client/) has the nextcloudcmd executable, but it appears to need a few other things installed from the package, such as libnextcloudsync.so. What platform are you running your server on? It looks like the packages are available on https://help.nextcloud.com/t/linux-packages-status/10216 for each service - given the Arch package is the "desktop client", it appears that it's possible to install the client on your headless server and still interact with it via nextcloudcmd