old man: For goyim the Meiri writes that. (And even in that case many seforim write that that was written in the Meiri for the Christian censors.)
But that is irrelevant for this case, as for Yidden everyone including the Meiri agrees Christianity is Avoda Zora.
And in any event, all the poskim agree it is strictly forbidden to attend a Christian church service. (It is even forbidden to go into a church sanctuary when there is no service being held.)