Freighter, wide body and specific narrow body aircraft listed here https://en.wikipedia.org/wiki/Unit_load_device
uses unit load device/cargo loader. Freighter and wide body always use unit load device/cargo loader except in the bulk cargo door. Some narrow body aircraft can use unit load device/cargo loader to save time.
This is an example of a unit load device/cargo loader being loaded on a Japan Airlines 747-400:
This is an example of a unit load device/cargo loader being loaded on a freighter aircraft:
When this is added, there should be a setting whether this aircraft can have unit load device or baggage. If these are both checked, one will be randomly sent after requesting baggage. If one is only checked, one that is checked will only be sent after requesting baggage.
FS2020 has one narrow body aircraft which is:
A320neo. This one can have both unit load device and luggage loading
FS2020 has two wide body aircraft which is:
Boeing 747-8 and 787-10. These can only use unit load device