>If it's not POTUS could it be something else dressed up as a regular bible?
Neither the Bible nor any book has any significance to taking an oath of office. Presidents have been sworn in without a Bible, or using a substitute for the Bible. Article 6 Clause 3:
But even though it's done so often, is it a requirement? The answer is, quite simply, no. It's the oath that matters, not the item
Is a Bible required to take the Oath of Office?
https://www.rocketcitynow.com/article/news/nation-world/do-you-have-to-use-a-bible-to-take-the-oath-of-office/525-9860ec72-6412-47e3-aff1-835860f28e43
Article VI Supreme Law
Clause 3 Oaths of Office
The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.
https://constitution.congress.gov/browse/article-6/clause-3/