Supported items types for aggregate functions only mentioned in source code:

value_type  - [IN] the type of values. Only float/uint64 values are supported.

https://github.com/zabbix/zabbix/blob/1bd328b6178e9817c294aa04f65da11979ecaaad/src/zabbix_server/poller/checks_aggregate.c

But there in no such information in documentation:

https://www.zabbix.com/documentation/current/manual/appendix/functions/aggregate/foreach