Ancient Greek society did not operate with a modern concept of race based on biology or skin color.

Identity was primarily Cultural and Linguistic (Greek vs. barbaros).

Greek sources, especially Homer, portray Aithiopes positively

describing them as pious, devoutly religious ( ευλαβής, ευσεβής)
and favored by the Gods

The backlash comes from projecting modern racial ideas onto Ancient Greece.

Ancient Greeks didn’t think in terms of biological race.

The modern concept of race emerged as a product of the colonial enterprises of European powers

from the 16th to 18th centuries which identified race in terms of skin color and physical differences.

Ancient Greek's main divide was Hellen (Greek: Ἕλλην) vs. Barbaros (language and culture), not skin color.

A Persian could be a barbarian - an African could be admired.

In Homer, Aithiopes (Africans) are beloved by the Gods

Zeus (Δίας) feasts with them.

Iliad 1.423–424:

Zeus is absent from Olympus because he has gone to feast with the “blameless Aithiopes.”

«Ζεὺς γὰρ ἐς Ὠκεανὸν μετ᾽ ἀμύμονας Αἰθιοπῆας / χθιζὸς ἔβη κατὰ δαῖτα, θεοὶ δ᾽ ἅμα πάντες ἕποντο.» (1.423–424)

Odyssey 1.22–24:
The Gods are described as visiting the Aithiopes at the edges of the world for sacrificial feasts.

ἀλλʼ ὁ μὲν Αἰθίοπας μετεκίαθε τηλόθʼ ἐόντας
(Αἰθίοπας τοὺς διχθὰ δεδαίαται, ἔσχατοι ἀνδρῶν,
οἳ μὲν δυσομένου Ὑπερίονος, οἳ δʼ ἀνιόντος),

Casting a Black actress as Helen does not conflict with ancient Greek concepts of identity .

It reflects modern racial thinking, not ancient Greek views.