Unfortunately Home Assistant never specifies the associated config if there is an error. Just check “your” config. The “details” are not saying anything either…very annoying!
Copy-paste the following template into the Template Editor.
{%- for x in integration_entities('mqtt') if 'rgb' in states[x].attributes %}
{{ x }}
{% endfor -%}
It finds all entities belonging to the MQTT integration, searches each entity’s attributes for an attribute named rgb and, if it finds it, reports the entity’s entity_id.
Assuming it finds an entity, you’ll know its entity_id and whether it’s one you configured manually or possibly it was discovered automatically via MQTT Discovery.
EDIT 1
Assuming it reports an entity_id, if the entity belongs to a device you can find the device’s name using the following template (replace light.foo with your entity_id).
{% set did = device_id('light.foo') %}
{{ device_attr(did, 'name') if did is not none else 'Not Found' }}
EDIT 2
The template is based on the assumption that the “rgb option” exists as one of the entity’s attributes. If the assumption is incorrect then the template will, obviously, report nothing.
Sorry for my late respond due to circumstances. I appreciate your help.
This template gave me some output but only items that don’t have own config like volvo2mqtt integration. It might be that the option is embedded in this integration. So it needs to be fixed in an update I suppose.
The template reported entities that are created automatically via MQTT Discovery (and they belong to Volvo2MQTT).
In other words, it identified the entities having an rgb attribute that was reported by the error message. It answers your original question of how to find the source of the error.
Please consider marking my post above with the Solution tag. It will automatically place a check-mark next to the topic’s title which indicates to others that the topic has been solved. This helps other users find answers to similar questions.
NOTE
If you want more details about the exact names of the attributes, you can use this enhanced version:
{%- for x in integration_entities('mqtt') if 'rgb' in states[x].attributes %}
-> {{ x }}
{%- for z in states[x].attributes if 'rgb' in z %}
{{ z }}
{%- endfor %}
{% endfor -%}