Sorry for that. Solution by Robert_Kanaan
Here’s a couple of ways to access the values:
{% assign doctor = product.metafields.vendor.house-doctor.value %}
<ul>
{% for key_value in doctor %}
<li>
{{ key_value[0] }}: {{ key_value[1] }}
</li>
{% endfor %}
</ul>
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Or access the key value directly:
{{ doctor['sustainability'] }}