Print field content as div attribute in views template
The code you linked is for normal data fields like text or number.

{{ row._entity.field_field_text.value }}


An image is a reference field, which has no value property, but a target entity. This has it's own set of fields. In case of an image the target is a file entity with the field uri, from which you can get the url with file_url().

{{ file_url(row._entity.field_image.entity.uri.value) }}


Or use Twig Tweak to generate an image style url:

{{ row._entity.field_image.entity.uri.value | image_style('thumbnail') }}