I have this same behaviour too.
Really annoying but it makes the iOS version pretty unusable with sites that require a login. Super annoying to have to go and lookup the password to then copy/paste it across. This is made even more difficult because the password manager is buried within the settings function rather than just one tap away.
Im on android and Im having the same issue lately, unable to interact with the stored login credentials popup for each given site , so I’m unable to select the current stored login and password that is presented to me to enable the login to said site