I recently purchased a used iPad Pro 11 and noticed battery drain of about 7 or 8% per day when it wasn’t in use. I always set up my iPads to maximise the battery life so I knew this wasn’t normal.
Even during the night, with the iPad in airplane mode, every few hours the battery chart showed that the level had dropped. It was a consistent drop and there was no sign of any app activity.
When I first got the iPad, it showed the last charge had been to 92% five weeks earlier, and it still had 81% left. That suggested it wasn’t a hardware problem.
I still tried a force restart, but I’m not sure whether that made any difference. The iPad was on 1% when I left it overnight so it wasn’t surprising that it was dead the following day.
https://support.apple.com/en-gb/guide/ipad/restart-ipad-ipad63d30b5a/ios
I saw a previous comment about Microsoft Exchange - I don’t use this - but I decided to delete Microsoft OneNote. It has always struck me as being a bit clunky and inefficient although that’s mainly based on using it on my MacBook. Syncing takes longer than I would expect.
Since then, the battery life has been fine. I’ve used it for 10 minutes, left it overnight, and it’s still showing a 100% charge a day later.
It might be worth trying a force restart, deleting any Microsoft apps and thinking about any other apps that might be misbehaving. I think it's much more likely to be a software than a hardware issue.
This is the guide that I used to maximise battery life -
https://www.macworld.co.uk/how-to/iphone/iphone-ipad-battery-life-3513323/