The following aggregation functions must support last_foreach() parameter:

• kurtosis
• mad
• skewness
• stddevpop
• stddevsamp
• sumofsquares
• varpop
• varsamp

For example mad(last_foreach(//key[*]))

It's supported by server and also documented at https://www.zabbix.com/documentation/current/en/manual/appendix/functions/aggregate:

Aggregate functions can work with either:

• history of items, for example, min(/host/key,1h)
• foreach functions as the only parameter, for example, min(last_foreach(/*/key))