My 2020 iPad Pro 12.9" runs quite hot when playing Hearthstone and the battery drains within ~4 hours. My iPad mini 6 (as well as my Android device) is running the game perfectly fine.
This issue has been present for a while now and was there before the last update as well. No other app is behaving this way. I’ve seen this happen with another game before (they addressed the problem and quickly resolved it with a patch).