Variant metafield type List of files return string

If I used
{{ current_variant.metafields.custom.hero_images | json }}
result
{"error":"json not allowed for this object"}
If I used
{{ current_variant.metafields.custom.hero_images }}
result
["gid://shopify/MediaImage/31079273267451","gid://shopify/MediaImage/31079273300219"]

If I used

{%- assign hero_list = current_variant.metafields.custom.hero_images | split: ',' -%}
{{ hero_list[0] | json }}

result
"[\"gid:\/\/shopify\/MediaImage\/31079273267451\""

If I used
{{ current_variant.metafields.custom.hero_images.value | json }}
result
["\/\/cdn.shopify.com\/s\/files\/1\/0200\/6358\/4356\/files\/Black_-_Desktop.jpg?v=1666336384","\/\/cdn.shopify.com\/s\/files\/1\/0200\/6358\/4356\/files\/Black_-_Mobile.jpg?v=1666336384"]

But if I use

{{current_variant.metafields.custom.hero_images.value[0]}}
or
{% for value in current_variant.metafields.custom.hero_images.value }}
{{value}}
{%endfor%}

result -
null

How to transform this list that looks like an array to an object?
Or how I can get access for index in list files?

No repository file or test is named. Start by reproducing the reported Liquid metafield snippets and inspect how list-of-files values are represented and accessed; completion would require a confirmed way to index or iterate the value, or a clearly documented limitation.