Create trigger expression or calculated item with count function that is double with some suffix. For example: host:item.key.count(#12,30.5G,lt)
You will get
Cannot evaluate function "host:item.key.count(#12,30.5G,lt)": "30.5G" is not a valid numeric unsigned value.
Zabbix will check if second parameter is uint number before apllying G suffix.

So the question is, why Zabbix checks that the number is an integer if item is integer? Why can't Zabbix compare integer and fractional?