Takeaway:
There are a range of beliefs in the U.S. Assume none of them are default.
One the rights highlighted in the Bill of Rights is the freedom of religion or religious expression. The United States sees itself as a "melting pot" of different cultures and often cites the "separation of church and state." The U.S. has a complicated history with this ideal, however, and it can lead to heated debate about the role of religion in policy and everyday life.
According to the Public Religion Research Institute (PRRI), as of 2020, roughly 70% of people in the U.S. identified with some form of Christianity, with several other religious communities growing over the years. Because there is no official state-endorsed religion, it can be taboo to assume someone from the U.S. believes or doesn't believe in a certain religion, and increasingly public holidays are portrayed in a more secular light. For instance, Christmas Day (Dec. 25) may be a national holiday, but "Happy Holidays!" tends to be viewed as the most inclusive greeting because of other religious celebrations that occur around that time (though this can also be controversial within religious communities).
As mentioned on the main page of the Religion section, there is the "speaker" issue, and given historical tensions surrounding the Cold War, the U.S. may be more sensitive to religious portrayals coming from officially non-religious nations.
Avoid making references to real-world religions in content
Do not assume your audience's religion. It's fine (and fun!) to create content based on national or secular holidays, but best to avoid specific religious holidays.
Do not make content that suggests certain religions are correct/incorrect.
Avoid sacrilege, as mentioned on the main Religion page.