I’m trying to create a custom ‘more-info’ popup for Lights (Lightgroups)
I believe that the default one is very good. Although some functionality like setting the color-wheel / temperature is 1 click too far away in my humble opinion.
Some additional function buttons Eg to trigger automations (Eg cine mode) or scenes specific to the light group could also come in very handy…
With browser_mod you can create your custom pop_up and the light-entity-card contains the color-wheel. For the actual code Home Assistant uses, you can go to the Home Assistant githhub repository.
Regarding your browser_mod popup, please post yaml code!
Regarding your issue with light-entity-card, I do not know how to fix it. It worked fine for me back in the days. Is this issue the same with an other light? (Maybe a non-IKEA one?)