Did you ever have any luck with this? I am experiencing a similar error when trying to configure a MQTT sensor and I am on 2022.11.3. Validation just spins and if I try to use developer tools to reload MQTT entities I get “Failed to call service mqtt/reload. ‘list’ object has no attribute ‘get’”. Then if I try to reload other types of entities (such as Template) I get a similar error message “Failed to call service template/reload. ‘list’ object has no attribute ‘get’”.
This is my sensor definition (lives in packages):
mqtt: sensor: - state_topic: "homeassistant/custom_devices/kitchen_scene_controller/button" unique_id: kitchen_scene_controller_button name: "Kitchen Scene Controller Button" qos: 0 retain: false