Sorry, below was in response to a different message, but it is still relevant. (but I see both threads are with you anyway!)
It is my understanding that the free basic version only has a limited number of styles.
from: https://clarivate.libguides.com/endnote_training/endnote_online
There are two versions of EndNote basic.
- The free version of EndNote basic has 21 styles and a limited number of filters and connection files. This version is available to anybody, with no other purchase required.
- The version of EndNote basic available as part of the Web of Science has thousands of styles and hundreds of filters and connection files. This version is accessible by those whose institution has a subscription to the Web of Science.
Those with the Web of Science subscription should also have an administrator who can edit and add additional styles.
If you have a local EndNote online Administrators, they have the ability to update Styles for their site if EndNote online access is provided thru an institutional Web of Knowledge subscription. If you have EndNote online access through your institution, you can contact your local Administrator to update existing Styles or upload new Styles.
The administrator (if you have one) should see here for instructions on how to add a custom output style: