use utf8 charset as 7.8.4 does not support utf8mb4

config/database/ox-tunings.cnf

@@ -35,8 +35,8 @@ binlog_cache_size = 1M
 sync_binlog = 8
 binlog_format = row
 
-character_set_server = utf8mb4
-collation_server = utf8mb4_general_ci
+character_set_server = utf8
+collation_server = utf8_general_ci
 
 # This was default_table_type previous to MySQL 5.5
 default_storage_engine = InnoDB