Missing "Skala Prinos" beach.
Source https://www.go-thassos.gr/about-thassos/places/skala-prinos-beach

Unable to answer "What’s the house number of this building?" for way/205781798 via StreetComplete 45.1:

Appartement to rent

Attached photo(s):
https://westnordost.de/p/105846.jpg

Shop=boutique

via StreetComplete 45.1

Attached photo(s):
https://westnordost.de/p/106006.jpg

Unable to answer "What’s the name of this place?" for node/2157573178 via StreetComplete 45.1:

Here is the shop bame

Attached photo(s):
https://westnordost.de/p/105835.jpg

What is this Geannikis beach POI doing here ?

It seems that the international name for that beach is "Agios Antonios"
Source: https://www.go-thassos.gr/about-thassos/places

Missing "Tarsanas" beach. Local name "Ταρσανάς".
Source: https://www.go-thassos.gr/about-thassos/places/tarsanas-beach

Missing beach "Agios Vasileios".
Source https://www.go-thassos.gr/about-thassos/places/agios-vasileios-beach

Unable to answer "What kind of building is this?" for way/209114903 via StreetComplete 45.1:

That building doesn't exist anymore

Attached photo(s):
https://westnordost.de/p/105727.jpg

Hairdresser

via StreetComplete 45.1

Attached photo(s):
https://westnordost.de/p/106007.jpg