Battery health not increased

We do not expect Battery Health to increase as all batteries deplete with time. You need not be concerned until hour Battery Health reaches 80%, at which time you should make an appointment at the nearest Apple store for a battery replacement. Check these links...

https://www.apple.com/batteries/maximizing-performance/

iPhone Battery and Performance - Apple Support

If you are referring to the recalibration of Battery Health for iPhone 11 specifically after updating to iOS 14.5, there was no guarantee Battery Health would increase. It just ensured the Battery Health was accurate, which could have increased, decreased or remained the same.

Battery Health will continue to decrease with every full cycle charge of the battery. That's what batteries do. The more they are charged, they lose their ability to hold the same charge as a new battery. When the Battery Health dips to 80% or less, it will be time to pay Apple to replace the battery in your phone.