Update Nethserver 8 via the CLI?

No, you should use a version tag like “3.17.1” instead of “latest”. See Releases · NethServer/ns8-core · GitHub for the latest release version tags.
See also Update Core NS8 - #3 by davidep

For example:

api-cli run update-core --data ‘{“core_url”:“ghcr.io/nethserver/core:3.17.1","nodes”:[1]}’