I am looking for a D8 solution to theme the table view mode. To start, I would like to remove the main title (the "Legend" tag of the html fieldset).

Note: I know how to use hook_inline_entity_form_table_fields_alter to add/remove columns, I would like to theme what is outside the table.

After the remove of the title, I would like to remove the headers of the table ("Title", "Status", "Operations"...)

In fact, if someone have a solution, I would like to get rid of this table view mode.. My final goal is to have a very simple view mode showing only one field and the 2 action button..

Here is the solution I found to remove the header and the title: this is to preprocess fieldset and table hooks

/**
 * Implements hook_preprocess_fieldset().
 */
function my_module_preprocess_fieldset(&$vars) {
  //Remove the fieldset title/legend for field_myfield
  //as it is a multiple value field, I check only the
  //first part of the id to target field_myfield
  if (strpos($vars['attributes']['id'],'dit-field-myfield')>0){
    unset($vars['legend']);
    unset($vars['legend_span']); 
    $vars['attributes']['style'][]='padding:0';
  }
}

/**
 * Implements hook_preprocess_table().
 */
function my_module_preprocess_table(&$vars) {
  //In my use case, I need to target only table that are 
  //generated by ief module. I use the first part of the
  //id to target it
  if (strpos($vars['attributes']['id'], 'ef-entity-table')>0 ) {
    //remove column headers
    unset($vars['header']);
    //adpat layout;
    $vars['attributes']['style'][]='margin:0;border-collapse:separate';
  }
}