Thank you fergusq and lieven for replying.

fergusq:

'elaDya'ngan is same as 'elaDya' ngan, a noun-noun construction meaning "inhabitant of Greece"

Initially, I thought the same. But I started wondering whether there
was this subtle difference:

{'elaDya'ngan} = someone born, raised, and living in Greece
{'elaDya' ngan} = someone living in Greece but who has come from another country

lieven:

Additionally, at qepHom 2019, Okrand said:
"{-ngan} is generally translated as "people of", but it's more generally
used to indicate a group of beings, not necessarily beings from a
particular place. "

Seemingly/apparently this means that the opposite of what I believed
actually happens. {'elaDya'ngan} doesn't refer only to people born and
raised in Greece, but to any other inhabitant too. And this shows that
indeed there's no difference between {'elaDya'ngan} and {'elaDya'
ngan}, as fergusq previously wrote.

No, that's not what it means. He's giving some wiggle room for, say, a romuluSngan who has never been to romuluS, but was brought up in a Romulan colony. Or a tera'ngan who was born and raised on the Moon.

So -ngan as an element of a compound noun means something like one of the group of people associated with living on/in. ngan as a separate word means inhabitant of. A human being is a tera'ngan, but the human's cat is not a tera'ngan, though it is a tera' ngan.

lieven:

Note that Okrand wrote is using a hyphen. That does not mean it's a
suffix per definition, but it shows that {ngan} is usually attached to
the origin of people.

This is very important indeed. The fact that 'oqranD chose to write
{-ngan} instead of {ngan}, proves that we can freely attach it to any
country/location/etc.

No, it doesn't prove that. Okrand may just have used the hyphen to indicate an element of a complex noun that comes at the end. It's not automatically an indication of productivity. I happen to think you can freely attach it, provided it keeps the people of meaning, but that hyphen isn't proof.

-- 
SuStel
http://trimboli.name