I've got Zante a week on Saturday....was supposed to be Kos but hotel closure enforced a change.
It's random testing on arrival in Greece I believe, and I've heard the lead passenger is the most likely person to be pulled up (if you're travelling 2+ on one booking)
I got pulled up for a test on arrival in Halkidiki last October but there wasn't any need to isolate in the room, could carry on with the holiday as normal and you'd only be contacted if it came back positive. Perhaps different destinations and islands had different policies though.
For anyone considering a jolly, Jet2 are almost giving away holidays to Greece at the end of the month/start of next.