Physical cash? How?

Bitcoin Local offers the opportunity to meet a seller at a physical location. Same with Local Monero. If you're planning to exchange $10M, you'll probably need a couple of bag-carriers, and perhaps some muscle as well.

You can also trade for non-physical "cash", e.g. local bank transfer via escrow. As far as I'm concerned, that's a cash exchange.

Won't the usage of escrow trigger a KYC/AML "event" of some sort? That would tie the two parties' identities in a way that a cash evades.

I think local traders are expected to execute some level of KYC. In my experience (under £1K, online) that's a photo of me, holding my driving licence and a piece of paper syaing "I'm buying X from Y". I've never tried a physical cash trade in person.

You arrange to meet someone online, meet up, exchange cash for btc/whatever, done.

Never had a bad experience with it. You just sit in a coffee shop with the person for the few minutes it takes for a transaction confirmation.

One simple option: Hand someone some cash, they send you some BTC

Not that simple. You need to validate the transaction on the chain and that takes hours

You only need a single confirmation these days. It takes 10 minutes.

Source: have been doing this for years.

How much do you pay on the transaction cost

Precisely this. There's nothing complex about it either. You get a bunch of cash, they get btc, or vice versa.

Presumably a Bitcoin ATM