[{"Items":[{"Key":"Key1","Values":[{"Value":"Value 1","EndDT":"2024-01-31T15:43:53.000Z"},{"Value":"Value 2","EndDT":null}]},{"Key":"Key2","Values":[{"Value":"Value 3","EndDT":"2024-01-31T15:43:53.000Z"},{"Value":"Value 4","EndDT":null}]}]},{"Items":[{"Key":"Key1","Values":[{"Value":"Value 5","EndDT":null}]},{"Key":"Key4","Values":[{"Value":"Value 3","EndDT":"2024-01-31T15:43:53.000Z"},{"Value":"Value 4","EndDT":null}]}]}]

db.collection.aggregate([{$match:{"Items.Key":"Key1"}},{$unwind:"$Items"},{$unwind:"$Items.Values"},{$match:{"Items.Key":"Key1","Items.Values.EndDT":null}},{$group:{_id:{_id:"$_id",Key:"$Items.Key"},Values:{$push:"$Items.Values"}}},{$group:{_id:"$_id._id",Items:{$push:{Key:"$_id.Key",Values:"$Values"}}}}])