After trying to change the campfire cooking recipes of raw items I noticed that minecraft:salmon seem to not be working as an ingredient.

Either my datapack usage is wrong (I have the same exact file structure for other recipes but those work exceptionally, salmon specifically does not) or there is something more going on. I will also attach the datapack in question for you to check.

Further investigation in this matter reveals the following:

1. Adding a salmon recipe through the data/crafting/recipes/<recipe-name>.json file does not work no matter what the file is named.
2. Using data/minecraft/recipes/cooked_salmon_from_campfire_cooking.json the changed recipe works correctly.
3. Using both of the above recipe changes for the salmon (with changes between them to distinguish them) the minecraft folder one takes precedence and ignores the other recipe.
4. If the data/minecraft/recipes/cooked_salmon_from_campfire_cooking.json file is an empty json object and also add a recipe through data/crafting/recipes/<recipe-name>.json then everything works.

All other food related recipes added are working correctly without having an empty json object for the original recipe. The crafting folder take precedence instead of minecraft folder.

I hope this helps...

Thank you for reading this through. Have a nice day!