It's more difficult to trademark stuff like style, there are certain rules of what can be trademarked; long story short, non-graphical representations need to be clear, precise, self-contained, easily accessible, intelligible, durable and objective.

Trademark also gives a more limited protection in some ways.

Yes they probably can be trademarked.

But a big question is why? Trademarks are very expensive.

It makes sense for a company logo that was AI generated, but spending 100K+ for very limited protection of a piece of art seems questionable.