Is it possible to separate salt from food, or at least convert it into something that doesn't taste salty?
Even if there is a method to extract salt from food, specially from apple crumble, it’ll probably ruin it.

The simplest way I can think of doing this is dissolving the apple crumble in water and blending it. Filter it and then boil the filtrate.

Given that every solid ingredient but salt is organic, when all the water boils off you should be left with salt and burnt carbohydrates, since NaCl boiling point is way above 1000 °C and a stove will reach 400 °C tops. Now, if you ever burnt sugar you know the caramel sticks to the pan, so if you’re lucky just add water again to separate the salt crystals from the burnt carbs and transfer it to a different recipient. Boil the water to get the salt.

You can add the burnt carbs back to the apple crumble but I don’t think it’ll taste like apple crumble again.