I also nominated my favorite series for (almost) everything where thought it applied: Reincarnated as a Sword, Failure Frame, & Trapped in a Dating Sim. Honestly I felt a little biased focusing on those three but hey, whatever. At the very least, let me try to justify a few of my claims.
For best art, I nominated KWKM (Failure Frame) and Llo (Reincarnated as a Sword). From all the light novels I have read, their art stands above the rest. The level of detail is striking and it often captures the specifics of the book as well. For instance, it's not uncommon for artists to keep the characters in the same outfits in every depiction. Or to have the art only loosely tie to the prose. Or have the art be more of a sketch than a full render. I don't feel that's the case with these two and it comes across like they're always giving 100%. Here are a couple examples.
KWKM:
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I love that it's not just a character on a plain background for this color insert, but really captures the whole scene. The dress is extravagant and the emotion on Seras' face is capture perfectly.
Llo:
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Llo's art style is, IMHO, extremely cute. Every depiction of Fran is both adorable and cool. They say you shouldn't judge a book by its cover but I got into Reincarnated as a Sword in part because Llo's amazing art captured my attention.
For best Duo, I just want to argue for my #1 pick: Fran and Teacher (Reincarnated as a Sword). Their relationship is the driving force of the whole series and in the latest volumes that hasn't changed. Their personalities are deep, the character development extensive, and despite being very different they mesh perfectly together and it never feels forced.
For best antagonist I'm also just going to argue my #1 pick: Goddess Vicius (Failure Frame). She was always an antagonist in the series but the volumes released this year really exposed the true extent of her depravity and maliciousness. Despite being a Goddess of unparalleled beauty, you end up loathing her entirely. I love that mismatch of traits.