My understanding is that Project 2025 is a product of The Heritage Foundation, which I have heard say is a kind of Conservative 'think tank' and has its origins in 1980's. It is not specifically for, or by, Donald Trump but, as I understand it, a list of procedures to develop policies that a Conservative President should follow. News outlets on the issue say Donald Trump was not one of the authors nor owns any of the content. Donald Trump, apparently, likes some of the proposals in the manuscrpt but dislikes others.
However, because it is Donald Trump campaigning for a second term in office then such a document is bound to cause 'waves'.