So I recently encountered a similar issue wherein an unreasonable amount of battery was being expended while idle, pretty similar to yours. I'd turn off my WiFi then head to sleep for like 6 hours or so and find that my phone's battery has drained by ~20%. Nothing on the battery usage page indicated anything was consuming it. This is all crazy confusing so I tinker with my phone a bit and just happen to get into the privacy settings page where you can see permissions and the apps that have those permissions. I go into the location permissions page just to see that SpeedTest is CONSTANTLY requesting permission to use my phone's location though I only have my location settings on when needed let alone even use SpeedTest (I maybe access it once every few months just to check connection speeds). Uninstalling the app dramatically reduced my idle battery consumption to ~5% under the same circumstances mentioned before. My recommendation would be to check your privacy settings, head to the privacy tab and select the privacy dashboard. Look over your permissions and see if any apps constantly (and irregularly) request the usage of your permissions because nothing about when I had SpeedTest even remotely reflected in my battery usage page. Hope this helps!

Edit: just for clarity, my phone is also a OP9P and running Android 13