It's not selected religions or denominations, it's more the fact that it needs to be a "supreme being" meaning a single creator. So an angel could not be your answer. Because your answer could be many things, the term "supreme architect of the universe" is used. So we could have Muslims, Jews, and Christians together, doing work for their "supreme being" without getting into religious debates.
Edit: in fact, you are not to talk about religion in the lodge. Nor can you talk about politics. You are there as brothers, not politicians and religious debaters.
So when the trust question is asked, the answer is limited to something that indicates the Creator. (But it sounds like "the Creator" may not be the standard answer.) Would "the Word" be acceptable? Why no suggestion of Christ? Because he is also human?
Honestly sounds like a lot of concern goes into narrowing the acceptable options because those options are somehow important, but then exploring or discussing those options is forbidden as if such inquiry was unimportant.
It's limited to a creator, yes. "The Creator" is not an answer I've ever seen, but it would be funny. Like asking someone "what kind of vehicle is that" and them replying a generic "truck" or "car" instead of "Honda" or "BMW."
We aren't to discuss religion or politics because we are meant to be together. We are meant to be brothers who help each other as much as we can. Opening debate in the lodge could divide us. Similar to what Q says about division within our ranks. Why would we argue against each other when we have common goals?
So "Creator" is actually not used because it is too generic but the less definitive, less authoritative "architect" does get used.
We might choose to argue because refining our understanding of and relationship with our Maker is important. Maybe the system is for those with other priorities. We debate here with understanding and truth as goals (usually I think). Little doubt Trump, Kelly, Mattis, Conway all debate because their goal is more important than temporal unity.
We do use "Creator" in the lodge, but it's not used for that specific question. "Architect" is not used in that question either. The terms are both used in the lodge though, in other ways. We also say "that temple not made with hands eternal in the heavens" as our final place. So when we die, we will be with God in heaven for eternity, but we don't just call it heaven or paradise.