where did I go wrong?

[livid path]

This is nothing to do with blueprints really. I think you are mixing entity selector with target switches. entities and target entities are different check the pinned poses here.
What is the original code that was working before you changed it, the original blueprint.

[rose compass]

https://github.com/niro1987/homeassistant-config/blob/main/blueprints/automation/niro1987/zha_ikea_tradfri_2button_remote_brightness.yaml

I don't think it is using a target entity selector

light:
      name: Light
      description: Select the light entity you wish to control.
      selector:
        entity:
          filter:
            - domain: light