AWS Cognito exclusive email case insensitivity (no user name)

Hi,

I want an AWS Cognito user pool to treat emails as case insensitive. From my research, this should be easily possible for any user pools created after Feb. 2020 (see related docs here). However, it looks like that in order to make emails case insensitive, "User name" must be checked.

In this configuration, there exists no option to edit case preference

When "User name" is checked, the option to edit case preference appears.

I assumed that even though the option doesn't show up for "Email", that the default behavior of case insensitivity would still apply, but it seems as though the emails are being treated as case sensitive. I am aware that setting the case preference for the "User name" option will apply to emails as well, but what if I don't want user names as a sign-in option (emails only)?

I came across a similar question asked here, but I could not find an explanation as to why the setting is restricted like this.