Restrict Usernames such as email addresses

Hi

How can I restrict certain usernames such as email addresses from being used on signup? I have tried plugins such as “Restrict Usernames Emails Characters” but they don’t work.

Any options here? If I cannot, I would the opt for being able to add an information notice next to the username field on the registation form to ask users to not use an email as their username on signup.

Thank you!