Conditional fields for the field type 'managed_file' is not working in Drupal 8
I don't know, if this as anything to do with managed files, but I think #options should look like this:

'#options' =&gt; array(
  'text' =&gt; t('Enter The Text'),
  'upload' =&gt; t('Upload a Text File'),
),


and in #states the options key, not the translatable value:

'#states' =&gt; array(
  'visible' =&gt; array(
    ':input[name="field_type"]' =&gt; array('value' =&gt; 'text'),
  ),
),


If it has something to do with managed_file, then this old issue is back:

https://www.drupal.org/node/1118016

You can check this by changing temporarily managed_file to file.