The SQL mode NO_AUTO_CREATE_USER was removed in MySQL 8.0, and it's no longer recognized.

https://dev.mysql.com/doc/refman/8.0/en/mysql-nutshell.html#mysql-nutshell-deprecations says:

The following features related to account management are removed:

Using GRANT to create users. Instead, use CREATE USER. Following this practice makes the NO_AUTO_CREATE_USER SQL mode immaterial for GRANT statements, so it too is removed.
Change your sql_mode to "STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION". I tested this on my sandbox instance of 8.0.11 and it worked.

Either spelling of sql-mode or sql_mode are both fine.

Using quotes or omitting quotes are both fine.