Also even if it was from custom-ui, it was in the core documentation at some point because that’s where I followed along from. It now being unsupported and the fact the custom-ui doesn’t offer this (from what I can tell) has remove that capability which would’ve resulted from under the hood changes
https://developers.home-assistant.io/docs/frontend_creating_custom_ui.html
The dead link was most likely the original I was folllowing many years ago