My device battery health is not increasing

It’s not supposed to increase. It only goes down.

If you have an iPhone 11, then iOS 14 might recalibrate the measurement and show a higher number. But that doesn’t mean your battery capacity has increased; it only reflects a more accurate measurement.

Your Battery Health will vary with usage. You need not worry until it reaches 80%, at which time you will need to make an appointment at the nearest Apple Store for a battery replacement.