so I received a religious book and did a search by ISBN to enter it into my TBR list. It was found that way, but when I went back to search to see if there were other versions, it couldn't find the book by title, author, or even when I added genre!

I would say. look the book up by isbn as you did the first time then look carefully at the spelling of the title. There may be a slight mistake in there somewhere that is causing the title not to be found.

Also, be sure to check if you have any genres excluded in the "Excluded Genres Selector" section of your Settings. If the book you are searching for has multiple genres associated with it (either correctly or incorrectly) and any one of these is on your "exclusion" list, it might not show up in  your search results. If you have any "exclusion" genres set, try disabling them (temporarily at least) and do another search to see if the book shows up.

Can you find it by searching now? If PBS adds a book to its database for the first time when you enter the ISBN, it does take anywhere from a few minutes to a few hours to update the search indexes so you can also find it by title, author, keyword, etc.

Also make sure that your search is not limited to just posted books or paperback books or something else that could be excluding it.