Currently no International trains to Greece You can go till Sofia or Kulata (near the greek border) by Rail :)

or you take a discounted Ferry from Italy to Patras and from there a included Bus/Rail connection to Athens  

and do you know when they’re will be trains??

@claraduthoo  there have been several post in this community (Juse the search option)

Nobody knows when the train returns

Thessaloniki - Skopje - Belgrade was last a summer only service
Nighttrain Thessaloniki - Sofia - Bucharest was last a summer only weekly service
Daytrain Sofia - Thessaloniki was last a daily service all the year

All are suspended since Covid :/

@seewulf , and do you know if it’s possible with an interrail pass of four days to not only use the trains but also the boat to go to Greece?

Of course but for a Globalpass the routes are often just discounted https://benefitsportal.eurail.com/?categories=1be1ba1c-80f5-4286-b255-3092f0d486cd