Unlike a suspicious-activity-report, a CTR involves no judgement about wrongdoing and the customer may be told it is being filed. Aggregation is the part people miss: several smaller cash transactions in a day are combined.
Deliberately arranging transactions to stay beneath the threshold is structuring, a separate federal crime carrying forfeiture risk, and it will itself generate a SAR.
Securities brokers see these rarely, since cash deposits are uncommon, but the obligation applies across financial institutions including money services businesses and some crypto operators.
Related: suspicious-activity-report, bank-secrecy-act, fincen, anti-money-laundering