I always assumed that most brokers manage stop orders internally and only send them to exchanges/MMs once triggered. Certainly I would expect this from reputable ones like TDAmeritrade. If I understand below article correctly, they are sent to MMs before triggering. Which means MMs actually know where the stops are! Someone please tell me it ain’t so.
https://alphacution.com/robinhoods-trailing-stop-orders-extreme-profitability-by-design/
https://alphacution.com/robinhoods-trailing-stop-orders-extreme-profitability-by-design/