The real default value of character_set_system is not shown in information_schema.SYSTEM_VARIABLES.

For example, see the following output on 10.6:

MariaDB [(none)]> SELECT VARIABLE_NAME, GLOBAL_VALUE, DEFAULT_VALUE FROM information_schema.SYSTEM_VARIABLES WHERE VARIABLE_NAME='character_set_system'\G

*************************** 1. row ***************************

VARIABLE_NAME: CHARACTER_SET_SYSTEM

 GLOBAL_VALUE: utf8mb3

DEFAULT_VALUE: NULL

1 row in set (0.001 sec)

The real default values are:

• Up to 10.5: "utf8"
• 10.6 and above: "utf8mb3"

This probably occurs because the code sets the default value to 0:

https://github.com/MariaDB/server/blob/mariadb-10.6.4/sql/sys_vars.cc#L787

And then the value is actually set during startup:

https://github.com/MariaDB/server/blob/mariadb-10.6.4/sql/mysqld.cc#L5454

Can the actual default be shown in information_schema.SYSTEM_VARIABLES?