Ooh, I would have loved an f/f version of this - although I did like Marcus’ dim golden retriever persona, which I think wouldn’t have worked so well for him if coded female. I gather the author is a Jamie/Brienne fan tho, and I don’t know Game of Thrones fandom at all; maybe it runs more het in pairings, but like you I’d be surprised if straight cis men in it were so common as to be unremarked.

I can’t think of any f/f books with fanfic writers in them, which seems a terrible gap in the market.