My wife and I are headed to Europe the end of this April from Texas. We are US citizens. picking up cruise from Piraeus. We have a 3 hour layover in Istanbul on way to Athens. Retrim direct from IST. We are business class and looking forward to IST Turkish Airlines lounge.

EES/IETIAS IS once again cpostponed. -- other than passports, any other entry requirements?

Just make sure your passports don’t expire within six months of travel.

Check if you need an e-visa for Turkey. Can't remember what the rules are nowadays.

EES should be introduced later this year on a staggered basis over a few months. Once it is completely working ETIAS will be introduced.
Can't come soon enough since EU citizens have to pay for the privilege of visiting the US, and have done for years, and now also for the UK, and both charge more than ETIAS will cost!