Mongodump with query not working after upgrading to 4.4

mongodump --host tiger:27018 --authenticationDatabase admin --username admin --password odsfsdgfdt --out /tmp/stgopl -d local -c oplog.rs --gzip --query '{ "ts":{ "$gt" :Timestamp(1617745839,1)}}'
2021-04-23T14:25:33.113-0700 Failed: error parsing query as Extended JSON: error decoding key ts: invalid JSON input. Position: 16. Character: T

Also further checking seems like using $timestamp yields different results

st:PRIMARY> db.oplog.rs.find({"ts" : { "$gt" : Timestamp(1617745839,1)}}).count()
172305
st:PRIMARY> db.oplog.rs.find({"ts" : { "$gt" : {"$timestamp":

}}}).count()
0
st:PRIMARY>