db={"orders":[{_id:ObjectId("63f381b50ee158b55cc82b1a"),a_name:"This is an example",b_tags:[ObjectId("640624f7dace963b6d2865c3"),ObjectId("640624f7dace963b6d2865c4"),ObjectId("640624f7dace963b6d2865c5")]}],"inventory":[{_id:ObjectId("640624f7dace963b6d2865c3"),b_tag:"This"},{_id:ObjectId("640624f7dace963b6d2865c4"),b_tag:"demo"},{_id:ObjectId("640624f7dace963b6d2865c5"),b_tag:"only"}]}

db.orders.aggregate([{"$lookup":{"from":"inventory","localField":"b_tags","foreignField":"_id","as":"b_tags","pipeline":[{"$addFields":{"b_tags":"$b_tags.b_tag"}}]}},{$match:{$expr:{"$in":["demo","$b_tags.b_tag"]}}},{"$project":{"id":"$_id","a_name":1,"b_tags":1}}])