Database
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Query
db.collection.aggregate([{"$project":{"arr_strings":["$settings.button.elem.title","$settings.list.items.title.content","$settings.list.items.sub_title.content","$settings.list.items.desc.content","$settings.list.items.button.elem.title","$settings.list.items.list.items.title.content","$settings.list.items.list.items.sub_title.content","$settings.list.items.list.items.desc.content","$settings.list.items.list.items.button.elem.title","$settings.description.settings.button.elem.title","$settings.social_list.settings.list.items.title",],}},{"$unwind":"$arr_strings"},{"$group":{"_id":"null","all_arr_strings":{"$addToSet":"$arr_strings"},}},{"$project":{"_id":0,"strings":{"$setUnion":[{"$reduce":{"input":{"$filter":{"input":"$all_arr_strings","as":"string","cond":{"$ne":["$$string",null]},},},"initialValue":[],"in":{"$concatArrays":["$$value","$$this"]},}},]},}},])