Is this level of battery degradation normal?

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.

That said, normally, a 10 month old battery should be over 90% unless you charge overnight and it is well below 20% by the end if the day, so there may be a problem with your battery. However, unless it says there is a problem in the Peak Performance section Apple won’t replace it under warranty until it goes below 80%.

The absolute best way to improve the life of your battery 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.

There’s nothing you need to do or should do until it reaches 80% or displays a “degraded” message. When it reaches 80% you should get your battery replaced. If it is still in warranty (or if you have AppleCare+) Apple will replace it, free. If it is out of warranty it will cost $69, which is still a bargain. Apple stores can usually replace the battery while you wait.