No, just because a segment is required doesn’t necessarily mean that every element MUST be present. If you don’t have a segment with at least 1 element in it, your process will bomb.
For example, on an Outbound Invoice 810, the IT1 segment which is the detail line may be a required segment, but that doesn’t mean you have to map all 25 elements. You can map 1 or 2 if that’s all you & your trading partner agree upon.
If you’re mapping an Inbound 810 and they are sending a required PO1 segment for the detail, you must map at least 1 element or the whole thing will blow up.