I have my own Resourcepack that I use for my own textures, which utilities both item and model textures, through Optifine CIT. However, I think that the elytra trinket slot will not be able to have Optifine cit textures. I was using the. Now, this resourcepack worked perfectly under normal conditions, but when in the elytra trinket slot, it converted back the vanilla model, as I think that Optifine CITs fail to render or something. If you could fix this bug, (if it isn't a bug, could you please add it in a feature), that would be the best! Thanks! (I submitted this as an issue to the trinkets mod, and they said it was the problem with this mod instead)

Versions
Trinkets: trinkets-3.1.0
Elytra Trinket: elytratrinket-fabric-3.0.0-1.18.1
Here are some images to show the problem.

Unfortunately, since Optifine is closed source there's not much I can do in terms of compatibility. As far as I'm aware, I don't have any way to interact with their CIT logic.

Would this be a problem with Optifine themselves or Optifabric?

Unfortunately, since Optifine is closed source there's not much I can do in terms of compatibility. As far as I'm aware, I don't have any way to interact with their CIT logic.