db={"products":[{"_id":"655c3285822c4a52150c30a7","name":"Bag Product","variants":[{"variant_name":"Test Case","attributes":[{"attribute_name":"My Slot","options":[{"name":"0.18"},{"name":"0.22"}]},{"attribute_name":"Test Slot","options":[{"name":"s1"}]}]},{"variant_name":"Full Case","attributes":[{"attribute_name":"Slots","options":[{"name":"0.18"},{"name":"0.22"}]},{"attribute_name":"Test Slot","options":[{"name":"s1"}]}]}]}]}

db.products.aggregate([{"$match":{name:"Bag Product","variants.variant_name":"Full Case"}},{$addFields:{variants:{$map:{input:{$filter:{input:"$variants",cond:{$eq:["$$this.variant_name","Full Case"]}}},as:"variant",in:{$mergeObjects:["$$variant",{attributes:{$filter:{input:"$$variant.attributes",cond:{$eq:["$$this.attribute_name","Slots"]}}}}]}}}}}])