When i attempt to create new cpanel account in WHMCS, the error was:

Module Command Error
(XID rhmp6k) The system encountered an error while attempting to rename the unmanaged MySQL database user “wruzicdv”: (XID b5up59) The system received an error from the “MySQL” database “mysql”: 1805 (Column count of mysql.user is wrong. Expected 43, found 42. The table is probably corrupted)

Possible solution:

The issue stems from downgrading MySQL from MariaDB 10+ to MySQL 5.6. It would appear these databases were moved from a server running MariaDB and placed in a server running MySQL 5.6. The mysql.user table has a column "is_role" in MariaDB and MySQL 8 which should not be in MySQL 5.6, hence the errors you received.

This issue can be fixed in the future by either upgrading to MariaDB 10.0+, or by dropping the is_role column:

mysql -e "ALTER TABLE mysql.user DROP COLUMN is_role"

Note: I have not used above mysql command, but instead used this command to remove the error:
mysql_upgrade --force -uroot -p