i lost 3% battry health after update ios

You didn't answer my other question. How many months have you owned your phone? Often, when batteries are brand new, they hold more charge than they may be fully rated to hold. Often, Battery health stays at 100%, then when the battery finally starts to reduce as ALL BATTERIES DO, a decline of 2 - 3% is perfectly normal.

Your battery is only 3% from perfect. There is nothing to worry about. NOTHING. And you need to get used to Battery Health decline, because it is going to continue. You can't stop it. When the battery in the distant future, reaches 80% or less, then you pay to have Apple replace the battery in your phone. You are a LONG way from there.

Your battery is better than average. I would expect it to be around 94% after 6 months. Batteries are consumables; they lose a little capacity every time they are discharged, then recharged. On average this works out to about a 1% loss for every 25 “full charge cycles” ( some will be a little more, others a little less). As one example, if you charge the phone overnight, every night (and that is what you should do; it is a best practice), it starts the day at 100%. If it drops to 20% by the end of the day before you charge it again overnight that counts as 0.8 full charge cycles (20% to 100%), or about 24 full charge cycles per month of use. For this example your battery capacity will lose about 1% per month. Of course, if the end-of-day level is higher than 20% the capacity loss will be a little less, and if it is lower than 20%, or you charge it during the day, the capacity loss will be higher.

The absolute best way to slow the decline of battery capacity long term is to enable Optimized Battery Charging (Settings/Battery/Battery Health) and charge the device overnight, every night. The battery will fast charge to 80%, then pause. During the nighttime pause the phone will use mains power instead of battery power, allowing the battery to “rest”, and thus reducing the need to charge the battery quite as often. The phone will resume charging to reach 100% when you are ready to use your phone; it will “learn” your usage pattern. If you enable iCloud Backup (Settings/[your name]/iCloud - iCloud Backup) the phone will back up overnight also, assuring that you can never lose more than the current day’s updates.

Click on the link to read 'About the battery and performance of iPhone 11 and later' --> https://support.apple.com/HT210557

How long have you owned your 12 Pro Max and what is the current Battery Health on it?

A decline of 1- 2% Battery Health per month is normal.

3% in 7 months is FANTASTIC.

Stop worrying. There is nothing wrong with your phone or your battery.