It’s called structuring, their systems flag it automatically for the most part. The easiest way to get caught is multiple deposits under 10k in a couple days but there are lots of patterns. Criminals think they found a loophole and then get deadass caught because the real rules are more subtle.

The definition of structuring states, “a person structures a transaction if that person, acting alone, or in conjunction with, or on behalf of, other persons, conducts or attempts to conduct one or more transactions in currency in any amount, at one or more financial institutions, on one or more days, in any manner, for the purpose of evading the [CTR filing requirements].” “In any manner” includes, but is not limited to, breaking down a single currency sum exceeding $10,000 into smaller amounts that may be conducted as a series of transactions at or less than $10,000. The transactions need not exceed the $10,000 CTR filing threshold at any one bank on any single day in order to constitute structuring.

https://www.money-education.com/resources/financial-planning-news-and-blogs/blog/129-structuring-cash-transactions-under-10-000-is-criminal

AML investigations and fines are a bitch, they definitely do care. However, I think it’s basically automated at this point. Tellers or even bank managers aren’t making spot judgement calls.