I have a battery drain too and I suspect Hue Bridge. See this post:
I think that Hue Bridge send too much requests on the network that affects battery. They have update the firmware in 2019 but it has no change (« We fixed an issue that in some situations Apple iOS-devices had shorter battery-life when HomeKit was paired with the Hue Bridge. »)
My iPad Air 4 lose 7/8% per day.
It seems that only the Homekit admin devices are affected.
I think that Hue Bridge send too much requests on the network that affects battery. They have update the firmware in 2019 but it has no change (« We fixed an issue that in some situations Apple iOS-devices had shorter battery-life when HomeKit was paired with the Hue Bridge. »)
My iPad Air 4 lose 7/8% per day.
It seems that only the Homekit admin devices are affected.