>Is it possible (just for example) to exchange fiat for crypto, or crypto for fiat, or indeed one crypto for another, without having to involve an "off-chain"*

>Is it possible (just for example) to exchange fiat for crypto, or crypto for fiat, or indeed one crypto for another, without having to involve an "off-chain"* counterparty which comes with no guarantees? Fiat exists inherently off-chain, so you can't not involve an off-chain as you put it, unless you count stablecoins (government or non-government issued) as fiat. Crypto for crypto or crypto for stablecoins you can exchange purely on-chain via DEXs. >In the fiat world it would appear one can do an exchange "old school" by going to a physical bank branch and exchanging [physical] fiat for fiat (USD to EUR or whatever) and not have to worry that the transaction is going to be halted half way through due to "temporary restrictions" leaving you unable to access your capital. When you involve a bank or brokerage or paypal you do face those same risks (but possibly to a lesser extent) with fiat.