Docu here https://mariadb.com/kb/en/mariadb-maxscale-2308-simple-sharding-with-two-servers/ states
"The database users should be configured according to the configuration guide."
pointing to https://mariadb.com/kb/en/mariadb-maxscale-2308-mariadb-maxscale-configuration-guide/

But on the indicated location I cannot find any advice how to create the user.

The correct location is possibly here:

https://mariadb.com/kb/en/mariadb-maxscale-2308-setting-up-mariadb-maxscale/#creating-a-user-account-for-maxscale

But when I create a user like this:

CREATE USER 'maxscale'@'%' IDENTIFIED BY 'maxscale_pw';
GRANT SELECT ON mysql.user TO 'maxscale'@'%';
GRANT SELECT ON mysql.db TO 'maxscale'@'%';
GRANT SELECT ON mysql.tables_priv TO 'maxscale'@'%';
GRANT SELECT ON mysql.columns_priv TO 'maxscale'@'%';
GRANT SELECT ON mysql.procs_priv TO 'maxscale'@'%';
GRANT SELECT ON mysql.proxies_priv TO 'maxscale'@'%';
GRANT SELECT ON mysql.roles_mapping TO 'maxscale'@'%';
GRANT SHOW DATABASES ON . TO 'maxscale'@'%';

Then I get an error like this:

2024-02-03 07:46:54 notice : Started REST API on [127.0.0.1]:8989
2024-02-03 07:46:54 notice : shard2 sent version string '10.11.6-MariaDB-log'. Detected type: MariaDB, version: 10.11.6.
2024-02-03 07:46:54 notice : shard3 sent version string '10.11.6-MariaDB-log'. Detected type: MariaDB, version: 10.11.6.
2024-02-03 07:46:54 notice : shard1 sent version string '10.11.6-MariaDB-log'. Detected type: MariaDB, version: 10.11.6.
2024-02-03 07:46:54 notice : Server 'shard2' charset: latin1_swedish_ci
2024-02-03 07:46:54 notice : Server 'shard3' charset: latin1_swedish_ci
2024-02-03 07:46:54 notice : Server 'shard1' charset: latin1_swedish_ci
2024-02-03 07:46:54 warning: Error during monitor permissions test for server 'shard1': Query 'SHOW SLAVE STATUS;' failed: 'Access denied; you need (at least one of) the SUPER, SLAVE MONITOR privilege(s) for this operation'.
2024-02-03 07:46:54 warning: Error during monitor permissions test for server 'shard2': Query 'SHOW SLAVE STATUS;' failed: 'Access denied; you need (at least one of) the SUPER, SLAVE MONITOR privilege(s) for this operation'.
2024-02-03 07:46:54 warning: Error during monitor permissions test for server 'shard3': Query 'SHOW SLAVE STATUS;' failed: 'Access denied; you need (at least one of) the SUPER, SLAVE MONITOR privilege(s) for this operation'.
2024-02-03 07:46:54 notice : [mariadbmon] Gtid domain id of primary has changed: 0 -> -1.

So documentation seems to be wrong. Further investigating is done...