I happened sat near one of the guys who did that when I worked at a bank. Basically any transaction that was slightly outside of normal he'd look at, look at who the customer is and go "oh yeah it's spring and the construction company is spending more on supplies just like every year, oh but what is Darla doing right now that looks odd? Jimmy's deposit for his new motorcycle got flagged but that's pretty obviously what it is..." You get the gist.

Also a high chance that every mobile check deposit photo gets reviewed by a human being too. I saw so many communications about scummy companies sending fake checks as marketing and people misunderstanding and trying to deposit them, or just blatant fraud that might pass an automated verification but is obvious upon human review

Banking is one of the few industries that still relies heavily on human review for basically everything because it's so heavily regulated. But also it's one of the few industries that hasn't super consolidated down to a handful of companies so you can quite easily go to a small community bank that's locally owned and operated. And that's also partially thanks to regulations as well. I remember the bank I was working at really wanted to open a couple of new branches but they were severely limited due to it being in a different state and some other laws that weren't fully explained to me