Battery health

As you have an iPhone 11 see this support article→About recalibration of battery health reporting on iPhone 11 series with iOS 14.5 - Apple Support.

If the recalibration has completed most likely the 100% was a wrong value, that was corrected by recalibration.

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), although it is not completely linear. 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.

Here is Apple’s much longer explanation→iPhone Battery and Performance - Apple Support