Template sensor showing "unknown"

There is no need for a triggered template sensor. This is redundant:

Templates are already monitored for state changes of the included sensors.

This will do exactly the same thing:

template:
  - sensor:
      - name: Weight Eq and Above Threshold
        unique_id: f700e52a-1304-4d47-8bea-5b2c8f4049fe
        unit_of_measurement: kg
        device_class: weight
        state: >
          {% set weight = states('sensor.bluetooth_proxy_miscale_weight') | float %}
          {{  weight if weight >= 80 else this.state }}
        availability: "{{ has_value('sensor.bluetooth_proxy_miscale_weight') }}"

      - name: Weight Below Threshold
        unique_id: 42e1e5c9-1476-4e8d-9e8d-9071021ebb4b
        unit_of_measurement: kg
        device_class: weight
        state: >
          {% set weight = states('sensor.bluetooth_proxy_miscale_weight') | float %}
          {{  weight if weight < 80 else this.state }}
        availability: "{{ has_value('sensor.bluetooth_proxy_miscale_weight') }}"