On a discovery phase item prototype without LLD.MACRO throws an error "Item key already exists". Even if there is only single item discovered, it is not created.

Did tests on all current LTS versions(4,5,6) and behavior is the same: No LLD.MACRO in item key - NO ITEM on discovery(not even single)

For now only workaround is to intercept lld by JS preporcessing and insert empty value to custom lld.macro. Then use id as parameter of a key. But it limits usage of items without parameters.

Test template with trappers discovery starting v4: lld-single_4.xml
Using overrides does not help - without LLD.MACRO - 0 items.
Tests templates(with and without lld macro in parameters) with overrides starting with v5: Template_Single_spawn_with_overrides.xml
Template discovers systemd services and assigns simple net.tcp.service checks to each discovered service. Overrides are great for automation, but current behavior limits the usage.

---------------------------------------- In case if this behavior is by design : --------------------------------------------------------------------------------
Could you please change misleading documentation, which states that we MAY use LLD.MACRO in prototype configuration. To must use LLD.MACRO in item prototype:
https://www.zabbix.com/documentation/current/en/manual/discovery/low_level_discovery/item_prototypes

A warning or validation could be also added to Frontend on prototype creation windows.