There are two database collation/character set combinations Moodle supports with MySQL (and MariaDB):
- collation utf8mb4_unicode_ci with character set utf8mb4. This is the recommended setting supporting the full Unicode character set but some servers still don't support the index size this needs in which case they must use:
- collation utf8_unicode_ci with character set utf8. This works but has some restrictions, notably that trying to use emojis will result in a database error.
So you probably need to change the 'dbcollation' in config.php to one of the above collations depending on the character set used by the Moodle database tables instead of 'utf8mb4_bin'.
If you need to migrate to the recommended utf8mb4 setting – the Environment report will contain a warning if this should be done – then you'll need to run the conversion scripts as Ken says.