Unfortunately it is slightly different. there is this -L option which is not in the 2019 version. here is the list of options:
Usage: Vectorworks 2021 Updater [options] [command]
Options:
-v, --version output the version number
-I, --installdir <installation directory> Set the installation directory instead of pulling it automatically
-S, --serial <serial> Set the serial number explicitly instead of pulling it automatically
-L, --locations <name:path> Set the update locations instead of pulling them automatically. The format should be a comma separated list of location key:path
The error I got seems to have originated from not using the -L option. But I don't even know what the -L option is for and how to use it.