"I've had my iPhone for 3 months and my battery optimization is already 99.9%. Should I ask for a refund or stop charging it at night?"Ugh - Cue the anxiety over battery over these forums. Honestly - these detailed metrics lead to so much worry.
A phone battery is a consumable. Use your phone as you need and replace the battery when it's done. It's like tires on a car - drive them until they need replacing, and get new ones when they are worn.