According to greekcitytimes.com, these are the requirements for traveling to Greece
Display a negative molecular test (PCR) for COVID-19, taken up to 72 hours before the scheduled flight.
Present an official vaccination certificate in English, French, German, Italian, Spanish, or Russian, proving that travelers have completed their vaccination for Covid-19 at least 14 days before the scheduled flight. The vaccination certificate must include the name of the person, the type of vaccine given, the number of doses & inoculation dates.
Present proof of recovery from Covid-19, valid as of 2 months after positive test result (PCR or Rapid Antigen test) up to nine (9) months before travel.
Upon arrival, all passengers will be subject to random obligatory Covid-19 tests.
Maintaining a safe distance is really important in Greece because Greeks don't have an amazing health care system and the population is really old. I only recommend visiting Greece if you're vaccinated and planning on staying very safe, wearing your mask, and social distancing. Ikaria is a beautiful island that's very unique. It's considered a "blue zone". You can read more about it here https://www.bluezones.com/exploration/ikaria-greece/