From when I worked in a bank a long time ago, values haven’t changed though:
Over $10,000 cash: file a CTR Currency Transaction Report. This is a routine procedure, the IRS probably doesn’t care if you do it once to buy a car or something but still needs to be filled out. The bank officer doesn’t “decide” to do this, they have to. Some businesses do this every day or multiple times, they aren’t doing anything illegal but are running a cash heavy business, and they know this. It takes a long time the first time, then is pretty quick with prefilled info.
Exchange an over $3000 money order, cashier’s check (has different names sometimes), or traveller’s checks: MIL, Monetary Instrument Log. Same as CTR, not necessarily a big deal. Though tellers may hate you if you buy traveller’s checks in 2022.
Which brings us to:
SAR Suspicious Activity Report. This one is not automatic and the bank decides whether you deserve one. The one memory that sticks out to me is when a guy was doing a cash transaction so we did the routine asking CTR questions. He balked at that and lowered his transaction to $9900 or something to avoid it. That leads to closing the teller window after they leave and filing a SAR. Sometimes people actually need high 4 figures in cash, it’s not necessarily suspicious, bank’s call. Doing similar transactions at different branches that exceed $10,000 in aggregate is considered suspicious, and may be reported if noticed.
Filing SARs wasn’t nearly as common as getting counterfeit currency (usually by an oblivious innocent customer) or bad checks (by a nefarious scamming customer). And one nice old lady I had to explain to her she was being phished.