I think it is up to the application to decide whether the identifier should be case sensitive or not, perhaps using Rails 7.1's normalizes attribute feature. Therefore the validation which Quo Vadis sets up (linked above) should take its case sensitivity from the application.
The identifier (e.g. email or username) has a case-insensitive uniqueness validation.
However when someone logs in, the account is looked up by a case-sensitive finder.
I think it is up to the application to decide whether the identifier should be case sensitive or not, perhaps using Rails 7.1's
normalizesattribute feature. Therefore the validation which Quo Vadis sets up (linked above) should take its case sensitivity from the application.