The Rambam rules regarding studying the ways of Idolatry (Avodas Kochavim 2:2):
סְפָרִים רַבִּים חִבְּרוּ עוֹבְדֵי כּוֹכָבִים בַּעֲבוֹדָתָהּ הֵיאַךְ עִקַּר עֲבוֹדָתָהּ וּמַה מַּעֲשֶׂיהָ וּמִשְׁפָּטֶיהָ. צִוָּנוּ הַקָּדוֹשׁ בָּרוּךְ הוּא שֶׁלֹּא לִקְרוֹת בְּאוֹתָן הַסְּפָרִים כְּלָל וְלֹא נְהַרְהֵר בָּהּ וְלֹא בְּדָבָר מִדְּבָרֶיהָ. וַאֲפִלּוּ לְהִסְתַּכֵּל בִּדְמוּת הַצּוּרָה אָסוּר שֶׁנֶּאֱמַר אַל תִּפְנוּ אֶל הָאֱלִילִים. וּבָעִנְיָן הַזֶּה נֶאֱמַר (דברים יב ל) "וּפֶן תִּדְרשׁ לֵאלֹהֵיהֶם לֵאמֹר אֵיכָה יַעַבְדוּ", שֶׁלֹּא תִּשְׁאַל עַל דֶּרֶךְ עֲבוֹדָתָהּ הֵיאַךְ הִיא אַף עַל פִּי שֶׁאֵין אַתָּה עוֹבְדָהּ, שֶׁדָּבָר זֶה גּוֹרֵם לְהִפָּנוֹת אַחֲרֶיהָ וְלַעֲשׂוֹת כְּמָה שֶׁהֵן עוֹשִׂין שֶׁנֶּאֱמַר וְאֶעֱשֶׂה כֵּן גַּם אָנִי:
Many books have been composed by the idolators on idol worship, as regards its principle and its rules and practice. These books we are prohibited by the Holy One, blessed be He! from reading altogether, nor to meditate therein or in part thereof. We are even not allowed to look at the likeness of such an image, for Scripture says: Turn ye not unto idols, (Levit. 19. 4). In the same sense Scripture cautions us: And that thou inquire not after their Gods; saying, How did these nations serve their Gods? Viz.:—that thou shouldst even not inquire into the manner of idol worship, although thou does not follow it, for such an inquiry might ultimately lead to practice, and to follow their example; as it is said: Even so will I do likewise, (Ibid). (Translation Sefaria)
Now the books from the George R.R. Martin known as Game of Thrones features elaborate mythologies, histories, and lore loosely based on real-life historical facts.
Included in the book are entire story lines built around deities ie. Lord of Light, or the Faith of the Seven etc.
There is a vast and enthusiastic wiki page that codifies and explains the background of each deity.
Is it permitted to read them according to the above quoted Rambam?
Furthermore, there is a famous argument between the Rambam and Rambam about whether Magic is real. The Rambam was of the opinion that they are fake (ibid. 11:16) the Ramban disagreed. Therefore, in the opinion of the Rambam, it should follow that whether or not the deity/magical element is in fact fictional or real should have no bearing on its permissibility.
Therefore why isn't there a separate prohibition to read such fictional mythologies?