Concern over rapid battery health decline on iPhone 14 Pro Max

Read this support article about iPhone battery and performance to learn about the battery health feature and what is considered normal performance --> iPhone battery and performance - Apple Support

To see the feature go to: Settings > Battery > Battery Health

"A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge." A degraded battery may display the notice: "Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity." If it is not at or above 80% "normal", consider contacting Apple about a battery replacement. --> iPhone Battery Replacement - Apple Support

According to the above quoted information, you could be losing almost 2% per month the entire first year before Apple would deem this to merit a warranty replacement.

No. If you battery health falls below 80 percent in the first year of ownership, Apple will replace it.

Battery health is an imprecise measure and you can expect to lose about 1-2 percent of health each month of use. Sometimes that will reflect slowly, and sometimes in bigger chunks.

The iPhone 14 Pro Max was discontinued almost 2 years ago on Sept. 2023. Your battery is 2 years old unless you replaced it recently.

It would be expected to have some degridation on it although 96% health is unusually high for a phone of that age.

As Muguy explained, the battery should degrade about 1% a month which would put it around 76%. I'm guessing whoever you bought the phone from either replaced the battery or had the battery reading "boosted" which means they reset the battery reading without replacing the battery which would give you a false reading.