The following list of books are the only ones I know of that deal with Polytheism in a theological/philosophical way. There aren’t a lot of books available on the subject, and there may be more that I just haven’t stumbled across as of yet.
The Deities are Many: A Polytheist Theology by Jordan Paper
A World Full of Gods: An Inquiry into Polytheism by John Michael Greer
Sacred Gifts: Reciprocity and the Gods by Kirk S. Thomas
Walking with the Gods by W.D. Wilkerson
The books above are ones that I personally own. Notice that most of these titles deal with Polytheism as a whole, rather than through the lens of a particular tradition. Due to the nature of Polytheism, it is much more difficult to find books written about Polytheism from a philosophical/theological position than it is to find books written about particular traditions or about particular deities.
If there are other titles that you think I should add to this list, please let me know. It’d be awesome to have a much longer list than this!