There should be a way to find out which ECC curve names are accepted by gpg.
Best would be to have a command to list them.
https://gnupg.org/documentation/manuals/gnupg/ (showing 2.2.5)
only has some documentation in quick-add-key, see https://gnupg.org/documentation/manuals/gnupg/OpenPGP-Key-Management.html#index-quick_002dadd_002dkey
And that does not list all algorithms nor does it point to a place or a way to get this listing.
Suggestion: add this to the --version command and change the documentation to mention this.