Relationship fields & Bricks -> no content to filter

For my products I want to select a brand. I used the relationship field for this and filled in the brands. So for every product I choose a brand from the list. With my knowledge, this is the best option.

Now I want to use this field as a facet filter. When I add the facet, it doesn’t show any value. Just empty.

Is this type of field not valid for facets? Is there maybe a better way for me to add brands to my products from a pulldown menu?