Disallow annotation with a category (instead of a class)?

Currently, if a category (group of classes) is selected, we can make annotations tied to this category. It would probably make sense to only allow classes to have annotations, and not categories.

In addition, categories are considered as "unique" classes currently. What I mean is that, normally, clicking on a class highlights the annotations of this class. But clicking on a category does not highlight annotations of all its sub-classes but rather annotations done specifically with the category, which is not very meaningful.

Correcting this will bring more complexity. It requires being able to disable annotations while a category is selected. I'm open to suggestions to how to improve this! Be it a small change or a complete rethink of how to use classes in the app.