I have the same problem after IOS update 16.1.1. I have a 12 mini and my brother has a 12, it happend the same to him.
After I called Apple Support, they confirmed it wasn’t anything wrong with the phone and redirected me to an authorized Apple shop to check my charger and my phone.
The Apple technician tried to hide the problem blaming my charger ( even if the charger is original 20W and it works with other iphones) so I left without any resolution.
The thing is that if I turn off the phone (after I read other posts here) it is charging slowly. It is also charging with the same cable in the laptop.
I also restored my iphone and the problem wasn’t fixed.
Don’t know what else to do, it just annoys me that Apple doesn’t make a statement regarding the issue or at least admit that it is a problem with the IOS.