Target selectors non-deterministic or broken?

Why have you limited the binary sensor to “integration: mqtt”? (I just would have thought it easier to any device_class: motion).
Anyway I don’t have any experience playing around with mqtt (I want to tho). But maybe this will solve your problem?

blueprint:
  name: Z2M - Motion lights
  description: Motion sensor triggered lights with night mode
  domain: automation

  input:
    sensor:
      name: Motion sensor to use
      description: Something something binary_sensor
      selector:
        entity:
          domain: binary_sensor
          device_class: motion

    target_light:
      name: Light (day)
      description: The light to turn on during the day
      selector:
        target:
          entity:
            domain: light

trigger:
  - platform: state
    entity_id: !input sensor
    to: "on"

action:
  - service: light.turn_on
    target: !input target_light

Use the Studio Code Server Integration, (if you don’t already) it makes finding bugs easier.