When KDP finally approves your book, and you go and search for it, you can not find it normally, if you are doing this right away.
The reason this happens, is Amazon is constantly indexing everything on their site, multiple times a day. They are adding new products, updating products already indexed, etc and so on.
So you have to be patient as it can take a couple, 3 or 4 days to show up.
Also keep in mind, if you are in a niche, with thousands, or tens of thousands other books, you may type in some of your keywords and can't find your book, or maybe it is on page 60 of search results, because others have done research and may have used the same or better keywords as you did, and you could have a hard time finding it.