We don't currently have an option to exclude particular types of foods from only certain meals, though this may be something we can look into as we further develop things.

For the time being, you can still accomplish this by excluding the food in general and using Recurring Foods to override this for a particular meal. For example, if you only want to see smoothies for your breakfast meal, you can go to your Food Exclusions and type in "smoothie" as a custom exclusion to keep this out of your plans in general.

Then, you could use the Recurring Foods feature to set up some of your favorite smoothie recipes to recur often for your breakfast meal. This way, these smoothies recipes would override your exclusions only for this particular meal, but you won't see smoothies generating elsewhere in your plans.

You can see more about how to use these features in the articles below:

How do I exclude gluten, dairy, or other foods I don't like/want to avoid?

Using Recurring Foods to incorporate more of your preferred foods