iPad battery drain when signed into iCloud

It’s been some time that I’ve been suffering from massive battery drain issues on my 10.5” iPad Pro. The battery will typically drain by between 50 and 80% in 24 hours.

My only good workaround is enabling airplane mode whenever I put it away. I’m now at the point of selling the thing, as that's not very practical and it’s always out of battery when I really need it.

Does anyone have similar issues or any further ideas of stuff to try? I feel like this is now beyond regular tech support routines, but perhaps I've overlooked something? ☹️

• The issue already happened on iOS 14 and persists as of 15.1
• The issue goes away when I sign out of iCloud
• The battery also stops draining if disconnect from Wifi or use airplane mode, it will then easily last a week or two.
• Battery stats in the Settings app show the Home app as main consumer of the last 24 hours (during which i didn't use it). This is odd as home hub, background refresh and bluetooth are all off (see below), it shows about 6 hours of screen-off use by Home. Even 6 hours shouldn't drain 70%, but who knows
• Battery life on my iPhone 13 Pro and previous iPhone 12 Pro seems normal even though they are / were on the same iCloud account.

Things I have so far tried unsuccessfully:

• Tried turning Bluetooth off (off, not just disconnect, there’s a few Bluetooth HomeKit light bulbs in the home and with Home app showing activity I figured I’d try)
• The iPad is disabled as a Home hub
• Background Refresh is off
• Wiped iPad and set it up as new (not restoring a backup). Works fine until I sign into iCloud, then the drain resumes
• Disabled any and all combination of iCloud services, especially Home, Photos and Keychain
• Signed out the iPad, my iPhone, Macbook and iMac out of iCloud and cleared sync caches on the Mac. Then gradually reconnected them.