I'll start with a few things that I don't think will be trending, then I'll give my answer. I don't think dark fantasy can be the next trend because reality itself is a little too full of conflict to support people willingly diving into gritty fantasy. For similar reasons, anything that takes itself too seriously will also be unlikely to trend. While Brandon Sanderson thinks that, perhaps, dragons will be the resurging next trend, I think it's unlikely.
If I had to put my money on something, it's episodic plot slice of life. I think we're seeing the beginning of that curve already. Frieren was incredibly popular, and Dungeons and Dragons (and TTRPGs in general) are on the uptick. So, specifically, we're talking about slice-of-life character-interaction style plots, where there is still progression towards some goal.
I think people currently are craving fun interactions with other people, while still desiring to feel like they're progressing towards some goal, since life right now frequently feels like the opposite (at least in the US, and seemingly in Europe). People feel disconnected, and that their neighbor could be a political enemy, and that (regardless of side), their country is progressing backwards.
