Currently if $lookup has absorbed $unwind with preserveNullAndEmptyArrays it is not SBE-eligible: https://github.com/mongodb/mongo/blob/e00c730185a6649209d9cd7e844ad89b21534e6e/src/mongo/db/pipeline/document_source_lookup.cpp#L959
We should support it as it is a common-case join.
- related to
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SERVER-116127 Audit plan generation in $lookup-$unwind
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- In Progress
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