Hmm but apple themselves said background running in the back isn't actually running, their ram is frozen, it's just there for u to access them easily when u need to, it doesn't eat up any battery tho.
Yeah I saw 40 60 75 too, but the most common is 40, because it's easier to charge on a real life day to day basis. I was thinking like maybe even 30 would be fine too, but no one mention that

Yes it doesn’t run. But notifications coming in, the background app refresh will kick in and I guess there’s where the battery usage is.

I did a test to disable notifications. So battery dropping 10% for me is normal in my use cases.

To me.. don’t worry too much. Enjoy using the phone.