Custom Block Twig: File field how to get direct link to file?
#item is as far as I know only added by the image field formatter, so it's unlikely you'll find it in other field types.

Instead you can use the block content entity to get field values, for example:

{{ elements.content['#block_content'].field_file.0.entity.uri.value }}


This works independently of field formatters and as commented by @Kevin also when a field is hidden.