The json function will convert any string to object allowing to access its properties
twig
{{ json('[1, 2, 3]')[0] }}
{# results in: '1' #}
{{ json('{"foo": [666, 1, 2]}').foo[0] }}
{# results in: '666' #}
{{ json('{"bar": "\u0063\u0327"}').bar }}
{# results in: 'ç' #}