hey hey loriwiese
i don't really think places will be closed, it's toward the end of high season cruising in the greek islands and it's harvest season for wine & olive oil, parties/festivals/parades. not only cruisers but people sailing or flying in which adds up the crowds to thousands plus many wanting to see the same activities/attractions.
maybe 10 years ago we did a greek island cruise from venice, one stop was santorini and it had 6 ships in port!!! total nightmare, don't need to go there again. it's a tendered port, long lines to go up cable car or walk up steps with donkeys and donkey poo. pushing and shoving/grumpy/peasy people/ packed like sardines walking down walkways hoping they had deodorant/mouth spray, restaurants packed/can't get into shops then the craziness back to ship. more unruly people. ships get in early and some stay till 9-10pm, an all day affair. we went opposite, into a church, down to some neighbors homes, mom & pop small restaurant for late lunch over the caldera, was so nice away from the crowds.
cruisemapper.com
site to check where cruise ships are. click unselect all ships, click ports, search port name, scroll to month 2026, click ships in port scroll down to see capacity and sometimes an OMG moment (could be 15,000-20,000 people) if you want to stay away from crowds, pick another island, we liked corfu and crete, was there for a day but did private taxi tour to see many parts of island.
good luck and have a great time
aloha