[{"key":1,"_id":ObjectId("615602280000000000000000"),"created_at":ISODate("2021-09-30T18:30:00.000Z"),"meta":{"class":"class1",}},{"key":2,"_id":ObjectId("615753a80000000000000000"),"created_at":ISODate("2021-10-01T18:30:00.000Z"),"meta":{"class":"class1",}},{"key":3,"_id":ObjectId("615764100000000000000000"),"created_at":ISODate("2021-10-01T19:40:00.000Z"),"meta":{"class":"class1",}},{"key":4,"_id":ObjectId("615776d00000000000000000"),"created_at":ISODate("2021-10-01T21:00:00.000Z"),"meta":{"class":"class2",}}]

db.collection.find({"meta.class":"class1"})