There's a nextcloud client cli
I discovered recently that nextcloud has a cli tool bundled with the nextcloud sync client.
nextcloudcmd [OPTIONS...] sourcedir nextcloudurl
It seems to only be able to sync once a local folder to a remote.
I stumbled upon this information while trying to figure out how I could sync a .kbdx on my personnal nextcloud. I had in the mean time moved on to syncthing. Interesting find none the less.