Battery health drain

There is nothing wrong with your phone and Apple will not consider replacing the battery under warranty, unless Battery Health dips to 80% or less in the first 12 months of ownership (in your situation, highly unlikely). You have to recognize that every time you fully charge your iPhone battery, its Battery Health will decline, little by little. This is what batteries do - ALL BATTERIES. A decline of from 1% - 2% per month is considered normal.

Things you should do to maximize battery performance:

1. Never let the battery fully discharge and avoid letting it go below 20%
2. Do, charge your battery at night when you sleep, every night
3. Do turn on Optimized Battery Charging in Settings > Battery > Battery Health
4. Stop obsessing over something which will continue to decline no matter what you do
5. When Battery Health does dip to 80%, be prepared to pay Apple to replace the battery
6. Read this link about Maximizing Battery Performance --> Batteries - Maximizing Performance - Apple

That wouldn't make a difference. Apple won't replace the battery until it has declined to 80% or less.

So, stop worrying about something you cannot change. And do pay attention to the tips I shared with you.

No. The warranty covers manufacturing defects, which can include many components in an iPhone. In your case however, there is no manufacturing defect when the battery is performing as expected.