In IOS 16 update i am facing lots of problem .most one is battery draining so fast. Imy device is iphone 8plus
There is lots bug and many features are not supporte on ios 16 in iphone 8 plus
Yours is an older phone, so I suspect that the battery may need to be replaced. Apple Batteries typically last 2 years with normal usage. You should make an appointment at the nearest Apple Store for possible Battery Replacement...