[{"_id":"oidfi","users":[{"_id":"q","tags":["a","b","c"],"age":20},{"_id":"q","tags":["x","y","z"],"age":30}],"type":"repo"}]

db.collection.aggregate([{"$unwind":"$users"},{$addFields:{"anyTagsMatched":{$gt:[{$size:{"$setIntersection":["$users.tags",["a","x"]]}},0]}}}])