Since Zabbix 6.0 all standard templates are flat and monolitic. However, Zabbix still ships parts of templates that previously were used for template composition but now are unused.
For example, prior to 6.0 the template Linux by Zabbix agent included Linux CPU by Zabbix agent, Linux filesystems by Zabbix agent, etc. In 6.0+, Linux by Zabbix agent includes all the necessary entities so there is no need for Linux CPU and the likes any more.
Please identify such unused templates and remove them. These are easy to find because most (if not all) do not have tags.