the fish fillet, in both cooked, and raw form, do not count as meat.

in medieval origins revival, if you pick a race that is strictly a carnivore, you can't eat the fish.

It's a modpack, it would be on them to fix it.

It is in the appropriate food tags.

it is not a mod pack, it is a single mod.

food from other mods show up just fine in the appropriate food categories. the food in this mod is the only one that doesn't behave as it should.

ill contact the devs for the other mod.

Origins mod carnivore uses the meat item tag.
https://github.com/apace100/origins-fabric/blob/1.20/src/main/resources/data/origins/tags/items/meat.json

Adding support would be as simple as adding the items to the item tag. https://minecraft.wiki/w/Tag#Item_tags

There you go :) Will be part of the next update.