@VinistoisR Have you updated to the newest 2021.5 release?
I have the same Z31 RGBW controller and ran into the same issue you did and most of it is resolved in 2021.5
I would highly recommend using the custom card “RGB Light Card” or “Light Entity Card” and not the built in card.
But either way using the first device in the list is what you will want to use.
In my case I frequently want to utilize the same light colors. So I use the RGB Light card and have buttons for each color.