A logic issue was addressed with improved state management. This issue is fixed in iOS 15.1 and iPadOS 15.1, macOS Monterey 12.0.1, tvOS 15.1, watchOS 8.1, Security Update 2021-007 Catalina, macOS Big Sur 11.6.1. A person with physical access to an iOS device may be able to determine characteristics of a user's password in a secure text entry field.
https://support.apple.com/en-us/HT212876
https://support.apple.com/en-us/HT212874
https://support.apple.com/en-us/HT212872
https://support.apple.com/en-us/HT212871