I checked the new feature of multi alereters by seeing the source code. But some outputs are not correct.

For example,
In alerter src/zabbix_server/alerter/alerter.c
294 zbx_setproctitle("%s [connecting to the database]", get_process_type_string(process_type));

New alerters do not connect DB.

300 zabbix_log(LOG_LEVEL_CRIT, "cannot connect to alerter service: %s", error);
339 zabbix_log(LOG_LEVEL_CRIT, "cannot read alerter service request");

It must be "alert manager service".

In alerter manager src/zabbix_server/alerter/alert_manager.c

1865 zabbix_log(LOG_LEVEL_CRIT, "cannot start alerter service: %s", error);

It must be "alert manager service".