when I want to sign up in the app in firedb for example '' Mark@ss and then I make the '' M '' small, they're completely two different users, I want it doesn't matter if it's capital or small it's the same
'' Mark@ss = '' mark@ss
Before to create a new user in DB, you need to validate if the email already exist in DB. In that check is where you can compare so that it is not case sensitive.
The blocks you are showing seem to check if there is any not allowed character.