Hi Jai 
My partner, Anthony, confirmed just today that TUI won’t be flying to Thassos in 2020. He called the Thassos TUI office again and they were able to confirm this time.
He announced it here:
Tui UK travelling to Thassos?
Our next bet is for the UK and EU to lift restrictions this summer so that you can travel here independently. We’ll keep an eye on these developments and keep you posted!