I saw a post covering this topic, but it was for 1.12 and I was unable to do something like this in 1.16.

I may not be understanding something here, could anyone please explain how should I go about implementing such thing for 1.16?

I think you may want to take a look at SpecialRecipe class and its sub classes, to see how vanilla handles things like duplicating banners, cloning written books etc...

Thanks, I'll take a look

So I managed to make it work, but it only works for singleplayer. When I try to join a server, the client throws 

Internal Exception: io.netty.handler.codec.EncoderException: java.lang.NullPointerException

I am registering the recipe here:

@SubscribeEvent
public static void onRecipeRegistry(final RegistryEvent.Register<IRecipeSerializer<?>> recipeRegistryEvent)
{
    LOGGER.info("Recipe registry!");
    SpecialRecipeSerializer<MusicCloningRecipe> musicCloningRecipe = (SpecialRecipeSerializer<MusicCloningRecipe>) new SpecialRecipeSerializer<>(MusicCloningRecipe::new).setRegistryName("crafting_special_musiccloning");
    recipeRegistryEvent.getRegistry().register(
            musicCloningRecipe
    );
}

And it is kept here:

@ObjectHolder("musicblock")
class Recipes
{
    public static final SpecialRecipeSerializer<MusicCloningRecipe> CRAFTING_SPECIAL_MUSICCLONING = null;
}

Could someone please tell me what am I doing wrong? I couldn't really find a good documentation for it.