In Rambam Hilchot Shabbat 20:14 towards the end, he states that it is a biblical prohibition to ask a Ger Toshav to do a Melacha on a Jews’ behalf on Shabbat. Does this apply on a biblical level rather than a rabbinic prohibition to muslims and christians in israel or abroad today?

It is a rabbinic level prohibition to ask a Non-Jew to break Shabbat on your behalf [Rambam Hilchot Shabbat 6:1], in 20:14 the Rambam refers to a Non-Jewish slave of a Jew.