I guess it's not entirely about Blackwater, but have you seen the documentary Dirty Wars? It's by Jeremy Scahill, who is the author of Blackwater, unless there is another book about that, which wouldn't be surprising. Should be at least tangentially related to Blackwater.
Erik Prince - the founder of Blackwater - running shadow diplomacy on behalf of Trump prior to 2016 has been written about but not really explored in detail. I can guess a few reasons why.