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
Essays on a Polytheistic Philosophy of Religion by Edward P. Butler
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!
A Polytheistic Life 
It hasn’t been written and compiled yet, but here’s another that will shortly be in the works: https://neosalexandria.org/bibliotheca-alexandrina/future-projects/ascendant-modern-essays-on-polytheism-and-theology/
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Also check out Dealing With Deities: Practical Polytheistic Theology (see here: https://amazon.com/Dealing-Deities-Practical-Polytheistic-Theology/dp/193819702X/
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I’ll add it to the list! I’m hoping to get some more titles so I can actually create a page on this blog for books that pertain specifically to Polytheism as a whole. They’re pretty hard to find, which I find incredibly frustrating.
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A Million and One Gods by Page DuBois.
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