try adding this condition:
automation:
- alias: Update Harmony input_select
hide_entity: True
trigger:
platform: state
entity_id: remote.poaka_lounge
condition:
condition: template
value_template: "{{ trigger.to_state.attributes.current_activity in state_attr('input_select.harmony', 'options') }}"
action:
service: input_select.select_option
data_template:
entity_id: input_select.harmony
option: "{{ state_attr('remote.poaka_lounge', 'current_activity') }}"