The problem is that you’re using the Greek mathematical symbols:
Those come from the Supplementary Multilingual Plane, and are out of bounds; you have no font that contains them.
Instead, use the Greek alphabetic symbols:
Using those, I entered the start of the Greek alphabet in a Label in Interface Builder and it works fine:
And of course setting the label’s text
to "αβγδε"
in code works fine too.
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solved Greek letters in iOS doesn’t work [duplicate]