Can this be fixed by adding new user with [email protected] and later edit the user and change the email address?

No. The username is currently reserved. Changing email address won’t help.

A new user was created but if you will try to find it then you will get 0 result.

No users found is displayed by WordPress while the user was created before.

Method 1: Delete database entry from PhpMyAdmin

Method 2: Delete database entry from terminal

mysql -u db_user -p

show databases;

use database_name;

select * from wp_signups where 1;

delete from wp_signups where user_login=’johnsmith’;