My understanding is that most authorities from before Protestantism were of the opinion that it is not idolatry for gentiles but is for Jews but I cannot say that I really ever researched that extensively as it has few practical ramifications.
It’s actually pretty complicated, since the idea of transubstantiation was not formally adopted in its current form until 1215, long after Rashi, the Rambam, and many of the Rishonim lived. (Tosafos Avoda Zara 50b describes loaves that are given to priests to supply them with food, he is clearly not referring to the Eucharist.) Whether the idea of transubstantiation was widely accepted before that date or not is debated by the Catholics/Protestants . The bottom line is that assuming that shituf is in concept allowed for a non Jew, Catholicism for a non Jew would appear to be more problematic than Protestantism as far as the Noahide laws are concerned; even if one were to accept the Catholic explanation of why what they do isn’t considered idolatry according to their faith, (without going into details) that idea might very well be a violation of the Noahide laws of Idol worship according to the Jewish faith . Ask your Local Orthodox Noahide Expert
