Hello,
Is your question related to adding them, or to showing/editing them in the UI? As of now, adding them is possible using the API - there's an example about adding glossary terms in the GitHub repository and you could extend it with custom properties. Displaying them in UI and/or editing them there is not possible at the moment (there's a feature request for that).
(Oops - this was meant as a response to
https://datahubspace.slack.com/archives/C029A3M079U/p1670235428220579, but apparently added as a standalone post instead 😞 ).